Roger:
If you haven't yet, consider checking
the Photoshop for Windows forum at www.Adobe.com. There have been several threads on this topic addressing your questions.
The jist is that most reports of problems seem to be related to older equipment (printers, scanners, etc.) that don't have updated drivers for XP or systems that don't have enough processor or RAM to support the demands of Photoshop or XP.
In most cases indications are PS6 and PS7 work fine with XP just as long as minimum hardware requirements are met and peripheral hardware is relatively current.
~DannyR~