If you would like to get involved in the development of IntelliJ IDEA, use the following info on what you can do.
Download IntelliJ IDEA 6.0.3 EAP
IntelliJ IDEA 7.0, codenamed "Selena" is currently being developed.
IntelliJ IDEA 6.0 Architectural Overview
There are a few newsgroups at our news server (news://news.jetbrains.com).
Most of the groups are replicated to the web-based forums (http://intellij.net/forums/index.jsp?cat=9)
Working with issue tracker