Hi Phil
Welcome to the forum

If you're going the Palm route and you have the finance I would definitely go for the Zire 72 - it's the best value and well give you the longest in-service life given the built in multimedia facilities thus giving students the ability to audio-visually record their work. Also I foresee a large growth in rich media applications being published for these platforms over the next 12 months (hint, hint)

A Windows Mobile device with similar spec would be more expensive.
I understand that you're Apple Mac based desktop wise. My experience of Documents to Go has been very poor on the Mac platform. The whole thing feels like a cludge and has wiped the PIM data on my Mac and Treo combination more than once so I'm assuming there's some kind of system mismatch here or an undocumented feature (legal term for 'bug'). Have you considered the Missing Sync from
Mark/Space? I'm just starting to use it now.
I'm not even certain that running Word / Excel style apps on Palms are a good idea, have you checked the equivilents from
GoKnow? The Docs to Go implementation of Powerpoint on Palm is a hoax by the way!

Hope this helps