I agree. A referb MBP, a 2.33 w/ X1600 would not be bad, but I would suggest a 2.2 with the 8600M.
Why do I say this?
First, the GPU: The fact is that most of these apps don't need to store a lot in the vram, so the 128MB of VRAM on the 2.2's 8600M is fine and the 8600M is a full generation better than the X1600, speed wise. If you were interested in gaming, I would recommend the opposite, for the money. When games fill up the VRAM, it doesn't matter how fast your GPU's core speed is, the video is going to choke.
Second, the FSB and RAM: The faster FSB on the 2.2 actually utilizes the dual-core architecture more effectively, which is good for apps like photoshop. These apps may not stress the VRAM, but man can they suck up system RAM, and you may someday want to go all the way for 4 GB, which could also extend the useful life of this computer to last the duration of your time in school.