I'm working on building a new machine. One question is where to get the OS from, im kinda convinced I want Vista Ultimate. I do have a valid XP liscence of XP, but I think id like to just purchase the full version. I've checked a couple places including tigerdirect.com and they have a version in the retal box which is part number: M17-2512 and they also have a version listed as Windows Vista Ultimate 64-bit DSP OEM DVD which is part number M17-7418. The OEM one is way cheaper, and I'm wondering what is the difference between the two??? I'm kinda thinkin that Microsoft offers the oem version to pc builders at a better price, and tigerdirect has chosen to extend that price to anyone wanting to purchase it, rather than just install it on machines they sell. Also, I'm not sure why that have it labeled as 64bit... they also have a 32bit version listed which I have no clue about. Sooooo, If the retail version of Ultimate is 64bit, and the OEM/DSP version tigerdirect lists is 64-bit, is there a difference between the two??? Thanks in advance for the help!!!