First, to avoid confusion there is no "JBoss Portal 5.0".
We had a project called JBoss Portal (latest release was 2.7) the archive project page can still be found here: http://www.jboss.org/jbossportal
Enterprise Portal Platform 4.3 (Our product for which you can buy support) was based on Enterprise Application Platform 4.3 and JBoss Portal 2.7 (Adapted)
In 2009 we partnered with eXo to work together on a single portal project which is known as GateIn http://www.jboss.org/gatein (latest release is 3.1 to differenciate from JBoss Portal numbering). It's a major improvement, there are still some parts from JBoss Portal, but most of it would be new to JBoss Portal users.
Enterprise Portal Platform 5.x (Our product for which you can buy support) are based on Enterprise Application Platform 5.x and GateIn Portal 3.x (Adapted)
You will find the EPP documentations here for 4.3, 5.0 and 5.1:
http://docs.redhat.com/docs/en-US/JBoss_Enterprise_Portal_Platform/index.html
Also since you seem to be an EPP customer, I would advise to use the customer portal instead of the community forum if you are looking for faster answers (We take PTOs but not our support team :) )