JBoss Portal 2.6.1 supports JDK 1.4 and JDK 5.
JBoss AS 4.0.5 supports JDK1.4 (and JDK 5)
JBoss AS 4.2.1 supports JDK5 only
JBoss Portal 2.6.1 supports JBoss AS 4.0.5 and 4.2.1.
So for you the good match is:
JDK 1.4 + JBoss Portal 2.6.1 + JBoss AS 4.0.5
Thanks Thomas for your quick response,
I shall download the binary version of 2.6.1 and the AS 4.0.5GA now and follow the instructions in the reference guide found in the portal download for setting up the portal binary on the application server.