Go with whichever one you like better. They will both do the job just fine. I know no one who has gone with a mac and regretted it, however i do know a lot of people who will never get one simply because OSX is a new operating system to them, although its not hard to learn at all.
I'm in the same boat you are. Except I need a fast computer as well for my major for 3d drafting. I use my 12" iBook in class every day, and it's 2 processor sets behind the current models and works flawlessly. My desktop rig in my sig runs xp and is my gaming and drafting machine. However the new intel iBooks will run xp and all windows programs perfectly. If you have to have just one computer the new intel iBooks, IMO, are the ones to get.
AMD Athlon 64 X2 4200+ @ 2.6
ASUS A8N-SLI Premium
2x GIGABYTE 7600GT Silent Pipe SLI @ 607/800
OCZ Platinum 2GB DDR 400 @ 220 2.5-3-3-5
Raptor 74GB 10,000 RPM