Windows cd key problem

I am trying to re set up an e-machines PC the a freind has completely buggered up (new install needed) but they have lost the recovery cd for the computer. Luckily there is a Windows XP home cd key on the back of the case, but I'm wondering what version it is. I have a win xp home oem disk which I tried to use with the key but it didn't work. I presume it isn't retail, could it be a corporate key? or do the serials vary from country to country (my disc is from canada and the pc is from the uk)?

anyone have any thoughts?

The only times I've had problems using different discs than the originals is when the key is for a version shipped with SP1 and the disc isn't or such. Ussualy though that should be stated on the key I thought.

The pc is pretty old, it should have been pre SP1, but I found somebody who has almost the exact same model and I'm copying their recovery discs. I'll reset the cd key afterwards.