ok, after much help from these forums (thanks all) I have decided to build a computer instead of upgrading my old one. My newest noob question is: (and I know this is a beaten subject) Do I need to use my old hdd in the new pc if I am going to attempt to do a repair install with a copy of an XP cd? Basically, I have a pc that has a preinstalled oem version of XP with the coa on the case. After much research, I can see that it is a crap shoot whether the coa will be accepted. I know MS wants you to buy a new version, but I would like to save some $$. When I have finished building the new pc, do I need to boot from my old hdd to successfully do a repair install? I would like to get a new hdd as well. Can I use the old hdd for XP and format a better one and use it for everything else? The other issue is that I purchased this PC off evilbay, so I guess there is a chance that it won't work no matter what I do. (although, I have updated XP since I have had it and there have been no problems) Thanks for the help. I wouldn't ask, but there is so much conflicting information out there, much of wich is dated. (keep in mind, I have never done a repair install before)

With XP it's unlikely the HD will boot up when it's moved to a new motherboard. If your compaq only came with a restore disk, that disk will be useless in the new machine as it will only work for the particular compaq model you have. If you have a regular XP disk you may be able to do a repair install once you've moved the drive. The installation may or may not accept the COA on the compaq. It's going to depend on the particular XP version. If you have an extra HD lying around you might try an experimental installation on that just to see if it'll take the number. The good thing is if the COA is accepted you may be able to register it with microsoft. That's because for preinstalled systems the COA sticker doesn't necessarily match the key in the registry. So if you never registered the compaq with microsoft their records will show it hasn't been used.

The good thing is if the COA is accepted you may be able to register it with microsoft. Not any more if the machine is OEM with preinstalled OS - effective Feb 28, 2005. Look here. i_XpUser

If I try to install and activate a key on a second pc and it fails, will I be able to still use it on the pc it came with? Is there a way to tell if my COA was registered with MS? I would be willing to try it on the new pc and if it fails, buy another copy. I just don't want to try to use the preinstalled coa with a copy of an install disk and shoot myself in the foot.

keep in mind, I have used ms windows update and I don't recall whether I had to put the coa in the first time.

XPPID is a utility to change your Product Key (25 character serial number) on an already installed version of Windows XP: http://ryan.ript.net/xppid/

If you're unsure how a repair reinstall will turn out, the best thing would be to clone the drive to another and then experiment with the clone. If the installation takes the COA but microsoft doesn't it's not as though MS paratroopers will be landing in your front yard. You'll just get a message that you can't use that key.