You can check out the developer guide on how to get the source code from
http://anonsvn.jboss.org/repos/jbossprofiler/branches/JBossProfiler2
If you are interested in helping out with the web ui, then do
ant web
The code is located under
src/main/org/jboss/profiler/client/web/
src/main/www/
You can look at the command line client for an example of how the agent should be invoked.
The web ui should basically have the same features as the command line client - so they can probably share a lot of code - the rest is up to the developer ;)
Feel free to start new forum threads about any questions you have with the development.