servlet can't identify absolute classpath to jdbc

[zb cong]

i have install the jdbc driver for sqlserver2000 under the "c:\jdbc" directory,and set the classpath to point to all of three jar files under it,the programs with "main" entry that access sqlserver works well,but the servlet that access database don't work,and it tell me "no suitable driver",then i move the jar files to "TOMCAT-HOME\lib",the servlet works well,i know that the files under the lib directory will be loaded when the tomcat start,but why the servlet can't identify the classpath with absolute path?