Having installed Windows Vista SP1, the probablity of you removing it is rather bleak. However, when you install SP1, Vista gives you the provision of removing it, in case you choose to do so in the past.
This is done, by keeping the old files that were replaced by the SP1 update. You can choose to uninstall SP1 at any future date as long as these files are intact.
However, if you wish to making Windows Vista Service Pack 1 permanent, then all you need to do is run
vsp1cln.exe in the command prompt window.
Just hit Y at the prompt and the files will be deleted. Windows Vista Service Pack 1 is now permanently installed on your PC.
Via: Digital Inspiration