This is a simple but effective registry hack that has been tried and tested several times by me and it works!!
If you don't believe me then try this for yourself!
1 - Start menu/run/ type "regedit" and press enter,
this will take you to the registry editor.
2 - Now follow this directory:
3 - When you get to WPAEvents in the righthand column there should be "OOBETimer"
right click it and go to "modify"
Change the numbers in there to :
FF D5 71 D6 8B 6A 8D 6F D5 33 93 FD (this works with Windows XP Home and Pro, both 32 and 64bit versions).
4 - When you've entered them, right click on the file "WPAEvents" and go into "permissions".
5 - In there highlight "SYSTEM" and underneath it check the two boxes under "deny" and click "OK".
Phew thats it!!! I know it looks complicated but it's really easy, it just requires patience.
To check that Windows is activated, simply click on Start menu/All Programs/Activate Windows.
It will say "Windows is already activated".