Your first choice is the Mac/PC debate. Being an art/photography major, a mac may actually be in the majority with the people you interact with on a daily basis. Try and find out what the "standard" is at whatever school you're heading off to. Beware that often enough the schools will only sell macs, because they're profitable to sell, unlike PCs. This doesn't have anything to do with who-uses-what.

If you go down the PC route, you've got two choices. If you've got the money, go for the corporate line of on of the major manufacturers. (IBM, Hewlet Paquard) If you're being "fiscally conservative", go for the best deal in the consumer line of any major company.

Have a geek friend work with you on picking out what features you want/need and are willing to pay for. (wireless networking, memory, processor, hard drive, and screen)

Matthew