Take it from me-- 1280x800 resolution is not very fun for photoshopping. YES, it can be done, I have done it for years-- but it is not optimal. I would say, if you have the money get the middle of the road 15" MBP with the dual graphics and Bootcamp into Windows. Use Windows for class, and enjoy OS X at your leisure.
I personally have been using my 13" MB as a desktop for 2 months... Plugged into a 1600x900 monitor and loving it. I would love 1900x1200. Plan on getting a Mac Pro in the fall and maybe running dual monitors at 1900x1200. Haha... But really, think about actual desktop size when you decide on the laptop... especially for what you plan on doing. Graphic design, animation, programming all require a lot of screen real estate, or at the very least benefit vastly from it.