Hello Sylvaticus,
If the copy of WinXp from your Friends is a Volume Licence version then you can change the Keys by following http://support.microsoft.com/kb/328874/en-us
If the copy of XP from your Friends is Not a Volume Licence version, then you will need to install a Volume Licence Version of XP to use your Volume Licence Key.
Thank you,
Darin Smith
WGA Forum Program Manager
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