Create a system restore checkpoint, in case you encounter a problem.
Start a registry editor (e.g., regedit.exe).
Navigate to the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\WPAEvents registry subkey.
Edit the OOBETimer value, modify any one character, then click OK.
Start the CD-ROM key Activation Wizard--click Start, Run and type
\%systemroot%\system32\oobe\msoobe.exe /a
Select the "Activate by Phone" option.
At the product key screen, enter your new key, then click Update.
If the wizard returns you to the previous window, click "Remind me later," then restart the machine.
Repeat Step 5. XP will display the message "Windows is already activated. Click OK to exit."
You can also use the following script that Microsoft provides to change the CD-ROM key:
****** begin cut/paste for ChangeVLKey.vbs
'
' Windows Management Instrumentation (WMI) Script - ChangeVLKey.vbs
'
' This script changes the product key on the computer. Service Pack 1
' must be installed.
'
'********************************************************************
ON ERROR RESUME NEXT
if Wscript.arguments.count<1 then
Wscript.echo "Script can't run without VolumeProductKey argument"
Wscript.echo "Correct usage: Cscript ChangeVLKey.vbs ABCDE-FGHIJ-
KLMNO-PRSTU-WYQZX"
Wscript.quit
end if
Dim VOL_PROD_KEY
VOL_PROD_KEY = Wscript.arguments.Item(0)
VOL_PROD_KEY = Replace(VOL_PROD_KEY,"-",""

'remove hyphens if any
for each Obj in
GetObject("winmgmts:{impersonationLevel=impersonate}"

.InstancesOf
("win32_WindowsProductActivation"
result = Obj.SetProductKey (VOL_PROD_KEY)
if err <> 0 then
WScript.Echo Err.Description, "0x" & Hex(Err.Number)
Err.Clear
end if
Next
**** end cut/paste ********
To use this script, go to the command prompt and run changevlkey.vbs <new key>
where <new key> is the name of the new key that you want to activate (e.g., ab123-ab123-ab123-ab123-ab123).
cf.