Apologies for my formatting, this is my first ever reply.
I've the same problem but with a Hp Scanjet G2710. I've made a CC4 package that deploys OK but, as you've found, pupils can't just connect the scanner and go. You need to be an admin for that...
However, if anyone plugs in a Scanjet 3400c it works straight away.
I wonder what is the difference between drivers that come with XP and those that are subsequently added?
...and yes, we've tried the approach where you dedicate a machine, or two, to be the scanning PC. However, in the Art dept they have scissors and they cut the cable-ties and move the kit around and then moan that it doesn't work.