can I use my XP disk on my friends puter?

[AMD6415]

my friend is having a bunch of problems with his computer and he was wondering if I could look at it and maybe reinstall XP for him and start new. Now the problem is he doesn't have his reinstall disk for XP anymore so I was wondering if I could use mine? I got it with my computer when I got it from Ibuypower.com and I have used it before but I don't know if I can use it on his because it asked for a license key thing... and mine was from Ibuypower.com and his is a gateway if I remember right. Its just a reinstall disk so that's why I'm thinkin it will work but then again it asked for the license so I'm not sure... will this work?

 

[Hefemeister]

If you have an oem copy of the correct version (ie home or pro) that matches the one listed on the serial key tag on his computer (assuming it has one. A gateway should) you will be just fine.

Of course you will use your disk with their serial. Not yours because that would not work as you cannot have 2 computers installed with your serial.

 

[james.wired]

Sorry man, that's illegal. One license per computer unless otherwise permitted by Microsoft.

edit: unless you go the way that Hefe said