Changing to a legitimate license key on WINXP

Good Day!
We have a WINXP but the license key is cracked, we bought a legitimate WINXP OEM cd and plan to install it over the cracked WINXP. The new WINXP is SP1 but our existing cracked WINXP is already SP2. I have checked with microsoft's website and followed their instructions on changing the license key but I get a general error.

Question:
1. How do I change the cracked license key to a legitimate license key?

Begin by opening the Registry Editor and navigating to
HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\Cu rrent Version\WPAEvents

In the right pane, right-click the ODBETimer binary value and select Modify. Change at least one character of this value to either a number from 0 to 9 or to a letter from A to F, then click OK and close the Registry Editor. This renders the current product key invalid and deactivates Windows.

Now, it’s time to reactivate Windows using your new product key. Click Start | Run and enter the command:
%systemroot%\system32\oobe\msoobe /a

select:
yes, I want to telephone a customer service rep to activate windows.
Click next
Select you location
Click change reg key and enter the new key
Then when it goes back to page wit the new ID key (8 sets of 6 digits)
Call the number provided and follow the automated instruction to get you conformation ID key.