I do my artwork almost exclusively in Photoshop; just switched from 7.0 to CS, and I think it's very user-friendly. (Earlier versions are pretty good, too -- I'm just spoiled on these.) With a little practice, you get the basics down quickly. The other plus is there's a wealth of tutorials online for everything you'd like to do with it.

I've never worked with 3D modeling software, but from what I've heard, it's not worth trying without a fairly fast computer to run it on. If you're still interested, a good friend of mine does 3D modeling for a living; I could put you in contact with him, and he could give you some more specific recommendations.