Tomcat comes with JAR files to support the
servlet and JavaServer Pages library classes.
You will also need JAR files for an XML parser - when I downloaded it the xml.jar was included, but they may have changed the one they are using.
You will also need the tools.jar file containing the compiler that comes with the regular JDK.
Do NOT use JDK 1.2.1 - use 1.2.2 or the new 1.3 JDK
If you have a previously installed JSDK - esp jsp.jar, get rid of all traces of it. I spent days tracking down a problem due to an old jsdk.jar on the classpath.