TechRepublic did a great job of documenting the removal of Windows Vista SP1 installation files. Here is an except from the site: "When you install Microsoft Windows Vista Service Pack 1, the installation process leaves behind about 800 MBs of original Windows Vista files–in case you later want to remove SP1. Relative to current hard drives, 800 MBs isn’t that much space. But, it’s still enough space to store a couple hundred MP3 files or a few video clips. Personally, I just don’t like useless files taking up space on my drives. In this IT Dojo video, I show you how to remove all those old files using the SP1 Files Removal Tool."
If you want more information, check out my article on this subject.