This must be common knowledge by now but since no-one has mentioned it ... after you install the Developer Tools, the generic *nix distribution of Tomcat (an environment for working with Java Server Pages) works fine on MOSX.
The one you want is in this directory on the Jakarta Tomcat site, and the particular file you want is jakarta-tomcat-3.2.1.tar.gz. The 'Mac-ported' .sea & .hqx versions seem to have a classpath issue & look as if they are actually running in MRJ, not under OSX (sorry, I haven't had a really good look yet).
The version above runs exactly like on Linux - ie. started & stopped with the command-line, so you get to see errors & messages. One problem, with http on MOSX generally though, I simply can't access localhost from browsers running under Classic!
Ashley
Mac OS X Hints
http://hints.macworld.com/article.php?story=20010412015142448