For simplicity's sake, P4 was designed during the time of XP (XP 64). To avoid driver issues, other non-compatibilities, etc. Vista 64 works fine with a 'modern' Vista raedy chipset and processor. I ran a P965 chip and an E6600 C2D on Vista 32 since the week Vista came out (almost a year). I ran Vista 32 beta on an Athlon socket A before that. Now I am running Vista Ultimate 64 on my current X38 Q6600. I think like others have suggested, you are better off having a modern Vista Ready system and you avoid having problems with 'ancient' hardware/software that was released before Vista was. For example, my cira Win98 printer has no driver for Vista 64, but still works when it's plugged in to Vista 32. Anyway, HTH.