I'm not sure how much difference the graphics card will make. But having been a starving Graphic Design student myself not too long ago my advice is probably going to go against the grain.
I would recommend a MacBook. Here's why: you are going to want to max out the RAM regardless of which system you get, you are going to want a quality scanner, and you will probably want an external monitor. Graphics apps (Illustrator, Photoshop) love a lot of memory. You are definitely going to want a scanner. Please, for your own sake, get a good quality one. Lastly, doing any work in Illustrator or Photoshop on a 13" screen is going to be an excruciating process, what with all the palettes and tabs and layers (much less actual files) running about. Having worked on a 15" it is merely bothersome. Working on a 19-20" monitor is much better, and hey, the graphics card will support it.
If you get a white MacBook, max out the RAM (say Crucial or the like), and get a good quality scanner you will end up at about the same price as a 15" 2 Ghz MacBook Pro. The computer will be more comfortable to carry to class (you may want to staple it to your shirt each morning), and less intrusive if you use it in your labs. You will definitely want the larger monitor for longer work sessions when you are back in your room. Adding a 20" monitor gets you up to around the price of a 15" 2.16 Ghz MacBook Pro.
Good luck, and don't sweat the critiques. They get better after a while.