*This process requires the Netdom utility
Download as part of the XP resource tool kit:
http://www.microsoft.com/downloads/details.aspx?FamilyId=49AE8576-9BB9-4126-9761-BA8011FABF38&displaylang=en
Or download just the netdom utility (scroll 1/2 way down the page)
http://www.petri.co.il/download_free_reskit_tools.htm

Here is the easiest way to rename a computer. This must be done from the server itself….

1. Click Start -> Run
2. Paste in this command – “Netdom RenameComputer OLD /NewName:NEW /UserD:domain\username  /PasswordD:password  /Force /ReBoot”. Be sure to change the text for OLD and NEW. OLD should be the current computer name and NEW should be the desired name.
3. Click OK

The computer will now automatically restart in 10 seconds with a new name.

Thanks to the original author