cannot activate servlet in the Web browser

OS=Windows98, Tomcat v. 4.1.27.exe, J2SE/JDK v. 1.3.1
contents of AUTOEXEC.BAT:
set PATH=c:\jdk1.3.1\bin;%PATH%
set CLASSPATH=%CLASSPATH%;.; c:\ServletDevel\database;c:\ServletDevel\database\lib\conn_pool.jar;c:\Tomcat\common\lib\servlet.jar
set JAVA_HOME=c:\jdk1.3.1

Compilation of servlet files that are included in this web application is successful.

Below is the content of Tomcat\webapps\database\WEB-INF\web.xml
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/j2ee/dtds/web-app_2_3.dtd">
<web-app>
<display-name>SL-314 Database Exercise #1 Solution</display-name>
<description>
This Web Application is a solution for Database Exercise #1.
This WebApp demonstrates a typical servlet design using Connection
Pooling and Data Access Objects to interface with a database.
</description>

<context-param>
<param-name>jdbcDriver</param-name>
<param-value>com.pointbase.jdbc.jdbcUniversalDriver</param-value>
</context-param>
<context-param>
<param-name>jdbcURL</param-name>
<param-value>jdbc

ointbase://@PB_HOST@:9093/WordGames</param-value>;
</context-param>
<context-param>
<param-name>jdbcUserName</param-name>
<param-value>PUBLIC</param-value> 
</context-param>
<context-param>
<param-name>jdbcPassword</param-name>
<param-value>PUBLIC</param-value> 
</context-param>
<context-param>
<param-name>minimumConnections</param-name>
<param-value>1</param-value>
</context-param>
<context-param>
<param-name>maximumConnections</param-name>
<param-value>5</param-value>
</context-param>

<listener>
<listener-class>sl314.web.InitializeConnectionPool</listener-class>
</listener>
<servlet>
<servlet-name>WordScrambleServlet</servlet-name>
<servlet-class>sl314.web.ScrambleGameServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>WordScrambleServlet</servlet-name>
<url-pattern>/wordScramble</url-pattern>
</servlet-mapping>
<error-page>
<exception-type>sl314.util.sql.ConnNotAvailException</exception-type>
<location>/error/server_busy.html</location>
</error-page>
<error-page>
<exception-type>sl314.util.sql.ShuttingDownException</exception-type>
<location>/error/server_shutdown.html</location>
</error-page>
</web-app>

I want this example web application with database activate the Scramble Game Servlet and run in the Web browser.
When I entered the URL http://localhost:8080/database/ for the message form in the Address field of Internet Explorer, the page for http://localhost:8080/database/index.html
below is displayed:

Duke's Arcade
Select from one of the following games:
�Word Scramble
When I clicked the Word Scramble above, the page for http://localhost:8080/database/wordScramble displayed the errors below:

Http status - 500
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
javax.servlet.ServletException
at sl314.web.ScrambleGameServlet.showCategories(ScrambleGameServlet.java:54)
at sl314.web.ScrambleGameServlet.doGet(ScrambleGameServlet.java:29)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2416)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:601)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:392)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:565)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:619)
at java.lang.Thread.run(Thread.java:484)
root cause
java.lang.NullPointerException
at sl314.domain.WordCategoryDAO.selectAllCategories(WordCategoryDAO.java:38)
at sl314.domain.WordCategoryService.getCategories(WordCategoryService.java:16)
at sl314.web.ScrambleGameServlet.showCategories(ScrambleGameServlet.java:43)
at sl314.web.ScrambleGameServlet.doGet(ScrambleGameServlet.java:29)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2416)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:601)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:392)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:565)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:619)
at java.lang.Thread.run(Thread.java:484)

Apache Tomcat/4.1.27
What do errors above mean? What should I do to correct those errors so to activate the servlet in the Web browser?
The topic is integrating web application with database, I�ve done nothing with the connection to the database management system, and I don�t know how will I do it. What DBMS should I have installed in my PC so to use for this?
Can anybody there help?
Any suggestions regarding this would be greatly appreciated.
Thanks in advance.
Regards,
Cathy

It requires a pointbase database, and if you don't already have it, I'm not sure how useful this app will be. It's not only the database, but of course, all the data inside of it.

How I can tell: in your web.xml file, there is a line that contains:
jdbc:pointbase://@PB_HOST@:9093/WordGames

You would replace @PB_HOST@ with the IP address of the computer that pointbase is running on (or 'localhost' if it's on the same box as Tomcat)