I'm not a Tomcat expert, so take this with a grain of salt:

First, I would recommend putting Apache in front, as I believe that it has better support for virtual hosting. However, the issue remains on how to point Apache to Tomcat such that a different "web app" gets called.

J2EE separates web apps (servlets/JSPs) into separate contexts ([link|http://host/context1|http://host/context1] versus [link|http://host/context2|http://host/context2]). This separates their class loaders/classpaths (though the classpath your referring to is probably for the who app server, itself). You should be able to configure Apache to point a particular virtual host to a particular Tomcat context.

Note that this separates each web app's class loaders, but all of the apps are still running in the same JVM. Basically, this means that "hosting" lots of Java web apps (as in a hosting service) is a major pain (the J2EE spec doesn't really support that kind of concept, which is kind of dumb), since it's possible for one web app to bring down the entire app server. At least, that's my understanding.

Dan