If like me you have been fortunate enough to get your grubby mitts on a copy of XP service pack 2, and have installed it and been somewhat annoyed to discover the "For testing purposes only. Build 2600.xpsp2" now loitering on your desktop above the time then you can remove this simply. This will probably also work for Microsoft Windows 2003 (not tested yet). To do this follow the next steps:

1. Open the Registry Editor click on the Start button on your taskbar, then click on Run and type "regedit" and click on OK to start the regedit utility.
    
2. Expand: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\CA\Certificates\FEE449EE0E3965A5246F000E87FDE2A065FD89D4 (see picture 1).
    

   Picture 1

   and

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\ROOT\Certificates\2BD63D28D7BCD0E251195AEB519243C13142EBC3 (see picture 2).
   
   

   Picture 2

3. And delete the pair of them, reboot and look, the testing message has vanished!
    
4. The modifications you made will be in effect after you reboot your PC.

Before making changes to your registry, particularly if you are following someone from the internets advice, make sure your data is all backed up and back up the branch of the tree that you made the changes on before you make them so that you can easily install the bit again. This way saves a lot of tears and tantrums.