I've got a couple of old, but very serviceable, HP scanners (a 4C and a
IIcx) that are not supported in Vista and for which HP will not be issuing
an updated driver. I found a third-party program, Vuescan, that has drivers
for hundreds of scanners. Though it is marketed as a stand-alone, i.e. it
can scan to a file or a printer, I found that Vista will use the Vuescan
drivers when I try to install the old scanners and, once installed, all the
HP-specific software (Deskcopy, etc.), as well as other programs that
support scanning, e.g. Acrobat, Photoshop, Word, etc., will work just fine.

I have nothing to do with Vuescan, other than I bought the software and I'm
thrilled that it will let me get more use out of my old HP scanners. Just
thought I'd share this tip.