Changing drivers appears to have worked, actually, it just took a little while for the effects to trickle through.

As for print credits, we sacked RM Print Credits off when it stopped displaying messages to users on XPSP2; went to Flo StopIt (also handles disk quotas) but that isn't S2008R2-compatible, so we're also on Papercut NG now. I really like it, and the client app which tells people what they're printing costs are is very useful.