Loading Windows on a new build

[Gary$1n2]

Not sure if this has been asked before, but here goes....

I'm building a new computer for my brother, and the only thing I'm waiting on is for a new copy of Windows XP to arrive by mail for the thing to be complete (should be here like Monday?), but in the mean time, can I load windows XP from one of my other genuine discs, and load all the updates, and then change the activation number when the new one arrives, or will I have to do a complete re-install when the new one arrives?

[EzyStvy]

Technically it's illeagal to do it...Hopefully we won't get in trouble...

The new cd/key code Must be the same Home/Pro AND OEM or Retail as the one you have.

DO NOT Activate the temp cd key you're using.

How to change the product key at the time of activation
http://support.microsoft.com/kb/810892/en-us

The free app has a built in key code changer:
Magical Jelly Bean Keyfinder v1.51
http://www.magicaljellybean.com/keyfinder.shtml

[Gary$1n2]

Thnx Ezy....only reason I wanted to do it is to get on with the build process while the Pony Express (USPS) catches up with me...lol! I really dont mind reloading everything, but just wondered if I could load Windows and then load the new product key after it arrives. No, I havent activated the former version, and yes, they will both be the same.
Again thnx for the info