Weblogic has its own vendor specific deployment descriptor for a war file(weblogic.xml) which has weblogic specifc parameters. If the app doesnt use any of those, the war wouldnt have any weblogic.xml files and it should just deploy fine with JBoss. Instead, if there is a weblogic.xml, you need to create a jboss specific deployment descriptor and bundle that with ur war file. The Developers could as well use XDoclet or some other code generation tool to create the Vendor specific deployment descriptors in which case you should be fine.
For the app that u tried on Jboss, try doing a
jar tvf someapp.war and see if you have a weblogic.xml listed in that war. That is most probably the reason it failed to deploy on jboss.
Hopefully this shud be a starting point for u to debug!!
How do I relate the Weblogic deployment descriptors to JBoss descriptors?
If they're sending you a standard J2EE package (no vendor specific descriptors) you should be fine. You can just drop it into the deploy dir. After that you can start adding JBoss specific descriptors if you need to optimize/customize the behavior.
If you get a package with weblogic descriptors you should still be able to deploy to JBoss. There might be some behavioral differences though. If foe deployer isn't able to correct them all, you're basically left with looking at both Weblogic manuals/DTDs and trying to find the matching tags in JBoss descriptors.