I'm not sure if I'm fully understanding. Just have your target set to OS 3.0 and Debug (either device or simulator) and you'll be debugging with 3.0? It's no different from debugging a 2.x application.
I am attaching a screen shot of the picture..is this the proper setting to debug using 3.0 SDk..?? I was hoping to see something like Ihone SDK 3.0 .!!!