I am not sure where your problem is coming from, but Portal 2.4 and above should be deployed on JBoss 4.0.4 and above, try this setup and report any errors you might encounter. Please include your full object.xml file and any related descriptors, as well as stack traces from the server logs.
As per your recommendation, I am installing JBoss 4.0.4 GA right now. If I encounter any errors, I'll follow up with xml files and stack traces.
BTW, I see that the jboss-portal-2.4.0-BETA1-src contains a file named portlet-instances.xml located in the following directories:
Is the portlet-instances.xml a new file for the BETA1 version or has it been included for legacy support?
If it is a BETA1 file, should the portlet instances be defined in the *object.xml file or the portlet-instances.file?
The reason I ask is because it appears the PortalAppDeployment.java source file (..\core\src\main\org\jboss\portal\core\deployment\jboss) has been revised in the BETA1 version to use the portal-instances.xml file.