I will wait a while from doing this in case I want to uninstall Vista SP1. Something I don't expect to need or want and disk space is not an issue so I will leave it there for now.
"Just open your Windows command prompt and type vsp1cln.exe (short for Vista SP1 Cleaner). It takes less than a minute to execute."
Around 800 MB will be made available.
Windows Vista Service Pack 1 Deployment Guide has all details the IT pro needs.
If you want to automate running the Cleaner here are the command line options.