So I don't have a XP cd and I used my friends cd.  I installed windows xp with his cd and I was never prompted for a key.  Now on my laptop I have a windows key on the back.  Here is my question can I change my key and register it? Will that change the WPA file?  Is that even legal(using anothers cd to install xp)? thanksusually when you use Friends cd's, as soon as you download windows upgrades you will get the authenticity problems. As far as I know the only way to change the key is to install a nother version of windows. My suggestion is to use your laptops windows DISK on your other computer to make it authentic.Unless your friend had a volume license copy of XP (would have been through a business if he did - and then for business use only) then it is most definitely a taboo to use someone else's disc and your key - if it even accepts it.

Usually the machine that comes with a key already stuck on, has had the OS pre-installed (and any 3rd party manufacturer applications along with it). If you were able to install XP using another persons disc you would have a 33% chance the key would be accepted - mainly because there are three versions of an OS disc.

Volume license - one key covers a SET number of machines (businesses use this type of key)
Retail license - a full copy bought off the shelf as a STANDALONE copy
OEM license - preinstalled on a machine (which it seems is most likely what you have if the COA is already on your laptop)

As long as you have an authentic certificate I don't think that the big boys will be kicking your door in, but it can cause ISSUES later on with Software Updates if the key has been registered on a different machine.