Vista SP1 includes a Files Removal Tool (VSP1CLN.exe) located in the Windows\Sytem32 folder. This is a command-line tool that will let to gain some disk space by deleting the archived files. The toll uses the following arguments:

VSP1CLN.exe [/h] | [/o: Offline_Windows_directory_path] [/quiet] [/verbose]

Where /h can be used to get help, /o is used when the archive files are in an offline image, /quiet runs in quiet mode without providing any console output, and /verbose provides additional diagnostics information.

You need to be careful when you run this tool and make sure that you have absolutely no issues with SP1. Once you use the tool to remove the files, you won't be able to uninstall SP1 from your computer.