I usually download the source for JBossAS 4.0.5 and build it with a 1.5 JDK - it creates both the regular binary and one that contains EJB3 support. I have successfully installed the Portal into the EJB3 version using the standard Portal installation instructions. I did this with Portal 2.4.1, but it should work with 2.6.
Thanks, I was working on getting the source for 2.6 CR2 downloaded while I waited for a response. I will build it and give it a try.