If you’re doing Photoshop on a Mac go Pro, you need the screen size and graphics card.
Go to http://www.macrumors.com it has heaps of good photoshop/photography forums and plus there’s a few bonus for mac users.
If you’re in the market for a new Macbook Pro wait till after WWDC07 (start of June) because Apple updates their product on a 180 basis and the Macbook Pro and the iMac are well past this so update will be very shortly.
Also check out the following links, great Mac purchasing tip’n’tricks:
https://guides.macrumors.com/Buying_a_MacBook_versus_MacBook_Pro
https://guides.macrumors.com/Buyer%27s_Guide