What method of deployment are you using? Packaged or expanded directory? I hate to ask the obvious questions but are you sure your
java classes are compiled in the WEB-INF/classes directory? Also have you defined your servlets in the web.xml file. If the answer is yes to both of these questions, then check your call to the servlet and make sure it corresponds to the servlet-mapping element in the deployment descriptor. If you are still at a loss, send us the following:
1. directory structure of the app
2. URL you are calling
3. copy of the web.xml file
Beyond this, I'd have to ask you what you mean by "not working". What error are you getting (404? 500?). Have you checked the server logs (or log4j file) to see if the servlet is actually being called and there is an error or if the servlet is actually not found?
We need more information than what you've given us. One thing I will tell you, Tomcat is working if you can get your JSPs to render. A JSP is a servlet after all.