I was always wanted to learn and work on J2EE framework since i saw it's market potential :). But only thing preventing me was the commercial Application Servers like WebLogic and WebSpheer which are not free. Good news!! I recently came to know about the alternatives to these commercial servers in Open Source community too. As following report says, they are really powerful. Go through http://www.adtmag.com/article.asp?id=6461 and make ur hand dirty with JBOSS(which seems the best) App Server if u r really interested in J2EE. Find ur customer and deploy their web application on such free s/w ;). This can be the best way to penetrate Open Source s/w among real users.
Regs,
-Dharmesh