Window XP Reacitvation if you overclock

I'm sure it won't be a problem... since Windows reads info from the CPU other than it's clock rate to determine if it's been installed on another computer or not. Just give it a try and see... worst thing that will happen is that you'll have to call Microsoft to reactivate. If that happens, try setting back to normal and that should work... but I don't foresee any problems.
 
If that's all you do, then I'm pretty sure you won't have to re-activate. The install can handle a couple of hardware changes before it has to re-activate, so you'll be fine.

Lyrics. Wasted time between solos.