500 gig is not a lot when you're talking about being in a college dorm. My guess is that you'll have a 2TB drive before your freshman year is out. Just wait 'til you meet the guy with 750 movies on an external and is willing to share.
But, I digress. The Pro is the clear choice here IMO. My reasons will obviously depend a little bit on major and school/campus, but for the most part they should apply:
1) battery life: if you have to walk a decent amount from your apartment/dorm to campus, you'll find that you stay on campus in between classes, so it won't need to work for just one hour at a time, you'll be away for the better part of the day (this will help your grades too). Sure you'll have time between classes, but you'll grab a bite to eat, talk to a friend or two, then you'll realize that it's time to head to your next class and you never stopped to charge your Air after your two morning classes...doh! If your major deals with any kind of science, you will eventually have a number of 3 hour labs, the Air won't make it through them and other classes. You'll quickly notice that the prime spots in the library/union/coffee shop/other study areas are the ones right next to the power outlets. During prime hours (not to mention finals time), it can get very hard to find an open outlet and you'll be cursing a 3 hour battery (this is the single biggest reason to get the Pro IMO).
2) durability: I love my Air, but my MBP just "feels" much more stable to me. You'll likely be shoving this laptop into a book bag with a number of heavy books. I don't trust the Air to take that kind of punishment and hold up over 4 years.
3) portability: The main advantage to the Air is portability; however, you're at one of the few places where I would argue that portability doesn't matter. Everywhere you go, you'll be lugging a book bag and a bunch of books anyways. Saving a pound or two is barely two couple chapters in most text books, so I don't think sacrificing battery power and durability is really worth it.
4) theft: Really any nice laptop could be the subject of a potential theft, so it's not like you'd be immune from theft with a MBP, but I'd guess that an Air would be more likely to be stolen. Just something to think about.
Good luck with school!