There are merits to both. It is true that it probably doesn't matter, however most web designers and creative types still use Macs. You would fit in better with one
. The mac has higher build quality than most PCs, and frankly is more reliable because of this. Unfortunately, you are also paying at least a 20% premium for the mac. Its your call if you want to purchase the BMW of computers (as Steve himself had called them).
You may also find it easier to be using whatever platform you use on school computers -- full compatibility is nice and helps with lots of little annoyances.
If you are interested in buying a laptop there are two more things to consider -
1 as suggested above, your college definitely will have software and hardware discounts on all types of PCs and Macs. Go ask. Those free Xbox offers that Microsoft does sometimes are certainly compelling ... as are the Mac ipod ones.
2 - Apple will likely release and updated ivy bridge line of laptops this month. Wait for those instead of purchasing now. Try to get one with discrete graphics. They will be more expensive, but for you discrete graphics should be worth it.