Camera/webcam required

Got a bit of an interesting one here, at work (school) I've been asked for some form of low cost document viewing camera aka visualiser.
i.e. something like this http://en.wikipedia.org/wiki/Document_camera but without the high price tag (in fact the 3rd image on that wiki page is the Lumens DC 160 which is the cheapest I've found at £250ish exvat which is better than the £800 which is a rough avarage price.

However that got me thinking, could we just use a high quality webcam connected to a frame or arm.
we don't need direct additional video feed (ie plugging it directly into the projector), as it would be used through a laptop so a teacher can annotate over the top with the interactive white board software.

What I'm not sure about is what I'd need to look for in a webcam for this purpose.

Projector res we work to is 1024x768, will need USB connection and some way of mounting it so we can have it pointing down.

So any sugestions to a good webcam? some other camera which could be used?

lol - and to thinkthat I used to reckon it was smart when my chem teacher projected his OHP notes onto a whiteboard so he could write on the whiteboard without messing up his overheads!

More likely to be, "Now let us all have a look at Johny's work and see what mistakes he made"
I did sugest a scanner but that's just a bit too slow, if you cannot have a picture up at once, without fuss, then student attentions wander.

Some days I think the simple methord of keeping them "enguaged" would be to electrify the chairs


EDIT: So what should I be looking for in a webcam?