When you re-install a Windows XP based laptop then the licensing is easy as just about every laptop that is sold will have a legitimate Windows sticker on its bottom. Trouble is that you might not have the right install CD.

To use that laptop sticker you need the OEM install disk. If you use a retail disk then the key will be rejected.

However you get the Windows XP installed you can get the correct OEM laptop key into Windows by running the program provided by Microsoft from,

http://windows.microsoft.com/en-US/windows/help/genuine/product-key

This program will update the product key and correctly set your product ID to match the key i.e. if it is a big-name brand then your key (and probably the BIOS) is decoded by Microsoft and the MPC (Microsoft product code) will be set to (probably) “76477” i.e. the Royalty OEM and the Channel ID will be set to “OEM” if you add a legitimate OEM key from the base of the laptop.

This also seem to correctly validate Windows.