finding windows xp activation key on existing installation [duplicate]

finding windows xp activation key on existing installation [duplicate]

The kid's computer is infested with viruses, and I want to wipe it clean and reinstall XP. I can't find the XP CD and box with the key sticker anymore. I have an installation CD from MSDN but for correctness reasons would like to use the original personal license. Is there a way to find out the activation key for the currently installed instance?