If sun portlet is JSR-168 compliant then you should be able to deploy it on JBoss Portal. You need to get rid of sun-specific descriptors and replace them with jboss portlal's descriptors. Please see our reference guide to see what descriptors you need.
I did a small how-to using Java Studio Creator and posted it on the Java Studio Creator forums: http://forum.java.sun.com/thread.jspa?forumID=881&threadID=5214100
which may help a bit as it took me a while to figure out the XML configs. Bear in mind, I've only made it work with v2.4 not v2.6.