Quick and Dirty method to change the cd-key in XP


Click Start > Run > and type in Regedit
Browse to HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\wpaevents

Double-click OOBETimer
Remove any part from the value. (Changing or deleting any of the binary values will accomplish the same effect)
Click OK and close regedit
Click Start > Run and type in: "%systemroot%\system32\oobe\msoobe.exe /a"
Choose the 2nd option (phone activation)
Click Change Product Key (at the bottom)
Enter your valid Corporate Product Key 
Press Update and close the window
Restart your computer

After the workstation restarts, click Start > Run
Type in: "%systemroot%\system32\oobe\msoobe.exe /a"
Make sure the dialog box says 'your copy of windows is already activated'