Oh, I also meant to mention ... you said you were trying to install with XP Home discs (at least some of them), but you said your license was for XP Professional ... Pro requires a Pro key and Home requires a Home key, as they are not interchangeable, nor is a "higher" key good for a lower version (Pro key will not work on Home). "I don't really understand why the Dell key does not work with a non-branded Windows XP Professional iso-disc. Is the Dell machine locked by both the original key and original media? Say, original disc destroyed before making a copy/image." XP was VERY picky with its keys.  Everything had to match - channel (VL, Retail, OEM), and each was keyed to accept certain keys.  Dell media would not work on other brands (not 100%, but in general), HP media would not work on other brands (which still holds true).  The OEM key always and only belongs to the system with which it was SOLD, and you had to have just the right media to use it.  Branded OEM disks would self/auto activate using a generic OEM SLP key embedded in the installation CD.  Generic OEM does not have that feature without the system builder using the builder/deployment toolkit to set it up. a) yes, you can use a copy of the installation disk - have done this many times (thankfully I no longer worry about XP) b) yes, you can do a clean install of Windows 7 regardless of the media type you get; Microsoft intended for you to use the Retail in your situation, not OEM - that's all I was saying there. "Another thing with the Retail version - I only need 7 for one specific machine, not 3" Not sure I follow that one ... 
Hello all - this is my first post!  I have a Dell Dimension e521 which came with Windows XP Professional pre-installed (genuine key and all). I bought this machine second-hand with no hard drives or Operating System/Driver discs. At first I tried using a couple of genuine oem Windows XP Home Edition activation keys I had lying around which work flawlessly on other physical machines or virtual machines. I also had an untouched oem disc of XP Professional, which, despite my genuine key, didn't work. When I tried to install XP Home OEM on a freshly arrived sata hard drive which I purchased off of eBay (I wiped it first with activekilldisk/dbandiskwipe) I could not get past the product key-window during XP-installation even though the same disc and same key had been used flawlessly on my Dell Inspiron 6000 laptop, among other scenarios (wiped clean). I also used the same XP Home oem disc combined with the inspiron key and this worked. I finally gave up, called Dell Sweden, told them I was not the original owner of the machine, that I had bought it as is and second-hand and they agreed to send me the original DELL Windows XP Operating System Disc for a small fee. When I used this Dell disc combined with the Product Key labeled on the computer case, it all worked!!  SO, to the question at hand; I want to buy a genuine OEM-edition of Windows 7 Home Premium x64, stick the Product Key label onto the top of the Dell case and install this instead of Windows XP Professional. Will I be able to do this or will Windows 7, like XP before it, halt at the product key/activation step? On a sidenote: As a pre-caution should the original Dell XP-disc get scratched or damaged I recently created a cloned image-file with IMGBurn and wrote the image to disc as a backup. Will my cloned copy be accepted or can the machine tell it's not the original?  Thanks!
DELL DIMENSION E521 + Windows 7