Why do you need it?
Clean Boot allows you to load in really clean Windows.
Clean Boot works in two modes:
To use Clean Boot DOS you need to activate Secure Start DOS.
Clean Boot for DOS is available only for Windows 95/98.
Clean Boot DOS works during DOS mode (autoexec.bat).
Clean Boot for Windows is available for Windows 95/98/ME/2000/XP/Vista.
Run Start Control, choose it in the main menu File->Go to Clean Boot.
When you want to restore to the previous state, RegRun will automatically offer to restore the Last Known Good profile.