You need the latest version of OS X to develop Apps for iPhone/iTouch (if this is what you'd like to develop for.) Will be hard if you're doing a PC.
But about the specs, you should be fine to develop Apps. On a 17" 2 GB Ram 2.0 GHz (?) C2D we do just fine.
Something like a Mac Mini would work fine for instance, unless you were doing very in depth games.