Installing the Service Pack 1 of Windows Vista generates about 1GB of files. These files allow you to perform resettlement in case of trouble but also to completely uninstall this update.

If you do not want to make one of these 2 tasks you can relieve your computer of these files by following this tip:

Windows Vista SP1 File Removal Tool (Vsp1cln.exe) Reclaims Disk Space

To run Windows Vista SP1 File Removal Tool, open a command prompt
(Cmd) or simply press “Winkey + R” keyboard shortcut. Then enter the following command:

Vsp1cln.exe

Once cleaning process completed, several hundreds megabytes of disk space will be freed, with reports saying around 800 MB, depending on edition of Vista installed. For advanced users,there are plenty of switches and options available to Vsp1cln.exe:

VSP1CLN.exe [/h] | [/o: offline Windows files folder path] [/quiet]

Code:
/? or /h: display Vsp1cln commands list.
/o:[offline windows files folder path]: location of Windows Vista offline image that wants to remove RTM files
/quiet: silent execution, no display.
/verbose: display extra details.
There is no download needed, as Vsp1cln.exe comes included with SP1. Note that once ran, SP1 cannot be uninstalled

Windows Vista SP1 Deployment Guide describes that vsp1cln.exe File Removal Tool as following:

Windows Vista SP1 File Removal Tool Vsp1cln.exe is an optional tool that you can run after you install SP1. This tool removes older versions of components that have been updated in SP1, which are stored during the installation in case you need to uninstall SP1 later. Saving these older components increases the amount of disk space used.. Typically, you should run Vsp1cln.exe if you want to reclaim this disk space after applying SP1 and if you will not need to uninstall SP1. You can use this tool both online and offline, but you must have SP1 installed. You cannot uninstall SP1 after you run this tool on an image.