If you have read my previous post about "How to Activate Windows XP Without a Product Key" I'm pretty sure that you will need to read this also. There is a possibility that you will receive a error message which says "This copy of Windows must be activated before you can log on" after 30 days. Since you have already activated the windows it will not allow you to go to the desktop. So what do you do to log back in ?
Boot into "Safe Mode".
To do this, turn the laptop on and press F8 as it is booting up.
Go into "Safe Mode" by choosing the "Safe Mode" option.
Once you are at the desktop in "Safe Mode", Click "Start" then click "Run".
At the run command prompt type the following EXACTLY
*NOTE: The "Oo"'s in Oobe are "oh's" - not "zero's" There is one space after rundll32.exe. It is case sensitive as far as I know.
Wait a few seconds - the screen may blip a few times or so.
This just reset Windows Activation for 30 days.
Reboot the PC into normal mode