Get a computer that supports 64bit, you will regret not getting a 64 bit computer if you want to use the newer version of After Effects. Also 64 for bit programs can use more memory, in a good way, if you are using a 32 bit computer and the program you are running use more then 2gb of ram then it will crash. Honestly, both Mac and Windows 7 both work fine so get what works for you. Macs do have a better color management but it is negligible in my opinion. The hotkeys are barely different, if you have half a brain. Working between the two(as long as you save as the standard files for both windows and mac which are is most files). You will have more difficulty working with older and newer versions of Adobe products then between the two OS.
I always liked working on my Windows 7 machine and printing off Mac.
Go for a macbook pro. I know people say PCs are just fine, but at a lot of art schools, they'll either laugh at you if you have one, or tell you to buy a different computer. Some places are so adamant about what kind of computer you have that they actually buy it FOR you.
Question! Which art school are you going to? I've done a ton of research on a lot of programs, so I might be able to tell you exactly what you're gonna need.
I dont think Savannah makes you have a laptop. I totally understand the need for one though. I'm going to Memphis College of Art. They had a similar policy on them. I got a macbook pro just in case. Using public computers just seems like a pain in the ass, you know? Considering you're going into animation, you need a lot of RAM.
I personally had a ton of success looking for a laptop on craigslist. I got my macbook pro for $800, and it works great. If you go that route, make sure nothing is fishy though. Make sure everything works, like the cd drive,usb drives, and run a system diagnostics check.
If you go the apple route, you might want to upgrade that RAM, and possibly hard drive space. Video takes up a LOT of space.