I need to upgrade several HP xw4400, xw4600 and one xw9400 workstations from XP Pro 32 Bit to the 64 Bit version. Most of them came with Vista Business downgradeable to XP Pro. We never used vista. Drafsmen are running into problems with an App and I believe the 64 Bit version with more RAM is the answer, since we aren't allowed to use Windows 7 yet. I received 64Bit media from HP (Gratis) and formatted and installed it on one of the xw4600s. Everything seems fine but it never asked for a product key and when I went to Windows Update it said I had to register. HP warned me that I may have to purchase an upgrade from Microsoft, not a problem, however I cannot seem to find where to do so. In addition when I went to www.microsoft.com/genuine and clicked on "Validate windows, it said validation incomplete and it listed all the versions it currently supports, Windows XP Professional was there, but not Windows XP professional 64 Bit?? I have about five of these I would like to upgrade for starters, so need to know how to do this first one. Any ideas?