Can I use the same copy to dual boot?

I would like to set up my computer to dual maybe ever triple boot with WinXP. I'm hoping that I could use the same copy of WinXP. it will be on the same computer and (obviously) only one being used at a time.
Would I have to get Microsoft to activate each install? or, is there a file I can copy to activte since it will have the same hardware config?

Yes