I would strongly reccomend spending the extra bucks on a MacBook pro for school.
Why? OSX. Unlike windows, you can use OSX without an antivirus and anti-spyware program. Due to the highly proprietary AND secure nature of Mac's software, viruses and hacking attempts are slim to none. As an added bonus, OSX suffers much less from "OS rot"; a seven year old OS9 install will work just fine regardless of how much pr0n you look at.
In addition, I would not be surprised if Apple upgrades the graphics with the next revision. From what I recall, each new revision of the "Snow" iBook brought a new video card, as did most of the TiBooks.