I second obgrahams' recommendation AGAINST an HP scanner.
A couple of days ago I installed the software needed to get one of their all-in-one units working on a system I "shepherd". Unfortunately one gets Image Zone even if you want only a Twain driver. The installation took forever and Image Zone should never be mentioned in polite society.
This system already had an HP flatbed with slide adapter. But the slide adapter holds the slides a millimeter or so above the glass. You can scan at 2400 pixels/inch to no avail since slides are slightly out of focus because of the bad design of the slide adapter. I hope the newer HP slide scanners don't have this problem.