I am an art student going into my senior year, so let me share my experience. I bought a MacBook (2.0GHz Core Duo, 2GB Ram) in the summer of 2006. Its a great computer, and is able to run everything from CS3 to Final Cut Express just fine. However, there were several things I encountered later on that made me regret my decision.
First off, screen size. While my MacBook only has a 13" screen, which is small, a 17" isn't much bigger when you're working with tons of windows. You're going to end up having to buy an external display regardless, at which point the screen size of your laptop won't matter at all (unless of course you DO end up taking your machine everywhere).
Which leads me to my second point. You probably won't take your machine anywhere. Any art class that requires computers will have them supplied, and they will be desktops that are most likely more powerful (and with larger screens) then your laptop. Not only that, but you'll begin to acquire necessary accessories that will become part of your everyday workflow that you will feel out of place without (external monitor, tablet, external drives, external keyboard and mouse).
All my problems have been solved now, as I have since purchased a Mac Pro.

Not to mention, art-friends I know have since purchased iMacs for many of the same reasons above.
I'll admit that it was cool to be able to move my MacBook the few times I dealt with the hassle of unplugging everything, but I could have gotten much more bang for my buck with a desktop machine. Of course, every user is different. Specifically, what is your art concentration going to be?