I want to dual boot my old Dell XPS gen5 with windows XP and windows 7 ultimate 64 bit, but my current processor is not x64 compatible. Right now I have a Pentium 4 Prescott 560 and I would like to upgrade to the Pentium 4 660 which from what I have read is basically the 64 bit equivalent to what I have now. They are both socket LGA775 so I can't imagine that I couldn't do it, but all of the places that I can find online to buy one from do not allow returns so I want to make sure that I get this right. Also my other concern is that I know dell is notorious for being a pain when it comes to the BIOS so I need to know exactly what it will take to pull this off. Thanks!