I would, for simplicity (I can't believe I'm saying this) use RedHat (Fedora Core).
This is the most commercial of the distros, IMHO.
You will be able to accomplish all of your tasks, from AD, to surfing, to word processing.
You can use samba to access your student shares...
Surfing is obvious....
Word processing, there is Open Office.org
However, the one thing that you would like to do, that I would refrain from, is CrossOverOffice.
Not only is it expensive, but it will crawl on those machines.
I installed it to a 866Mhz/128MB box, and it took forever for the simplest of things.
On my P4 box, it hauls ass.
Best of all - Linux is free - no license worries.....
Personally, I have to also throw out the possibility of using Slackware.
If you have any UNIX knowledge, as an admin, you'll be fine.