You can get a MS SQL Server thin Driver
here, or you can use the
Sun JDBC Driver search to find other Drivers.
You don't need to make any changes to the server.xml, you just need to change the class loaded in your Class.forName() line to the MS Driver, change the dtabaase URL to refer to your database, and place the JDBC JARs in the WEB-INF/lib directory for the web application.
Any JDBC sample code will show you how to connect, you just have to change the two parts listed above.
Dave