ok, an update:
Muchas gracias, folks, but I figured out (sort of) the troubles:
1. The USB drives now work. I made the regular user a "Power User" and also after a bit of hunting through the Security settings and stuff for user privileges, I found some that said "Formattind and removing removable media" or summat was allowed only for Admins. I've modded that to Power Users too, and voila!
2. The printer thing seems to be more an HP driver issue with Win XP Service Packs 1 & 2. For SP2 the solution is simple, you fiddle around with the Data Execution Prevention thing and everyone says it works. However I have SP1 - DEP came about only with SP2 - and there seems to be no fix. So short of getting hold of Service Pack 2 (*cough*not easy...ideas?*cough*) I can't print anything in regular user mode. So all printing work is now bunched together and when the time comes we log off and on and print en masse.