Or if you want a PC....
I've been selling college laptops to folks like you for months straight now. This is what I have always recommended. You want something to last you for the four years you'll be in school, not some cheap pos. Make sure you have:
Atleast a Centrino or Turion processor (no celerons dammit!)
1gb of ram recommended
HP/Compaq have pretty reasonable prices, I generally recommend them. Check out this unit here:
Choose either an Intel or AMD proc and then configure it to the above specs. If you're not sure which brand of proc to go with I recommend AMD. The Turions are 64-bit so they'll work better with applications that will come out in the next 1-2 years as well as Windows Vista (if you even upgrade to that). They also run cooler and can be less expensive. But it's really up to you which way you want to go.