Vista's Disk Cleanup utility has a "hidden" disk cleanup utility that gives you access to additional space-recovering, speed-booting options. Called cleanmgr.exe, you can use this utility for advanced cleanup, to get rid of old installation files, error files, unnecessary upgrade files, and any checkdisk (CHKDSK) fragments that may be stranded on the hard drive.
These advanced cleanup options are maintained and managed via settings that are stored by a feature called a System Agent, or sage for short. You can use the System Agent (sage) to set your options, by creating a sagest. Vista will use the settings contained in the disk cleanup sagest to determine the particular files you want it to delete in a disk cleanup.