Different methods to uninstall Service Pack 2 from Windows XP:

Method 1:

1. Open Control Panel and navigate to "Control Panel\Programs\Programs and Features".
2. Select the service pack 2 and click uninstall.


Method 2:

1. Open Command prompt in admin mode.
2. Type the following command to uninstall the hidden files,

         c:\windows\$NtServicePackUninstall$\spuninst\spuninst.exe

This step will allow to uninstall the SP2 completely.