Myself, I use CCleaner and something I've used from my Win98 days, "Easycleaner". Easycleaner is not quite as rigorous as CrapCleaner but does a good job for me. Right click and run as Administrator. Look at registry and unnecessary files I've not looked at Win7 as I've not had problems with a full HD but XP had a load of leftovers( Uninstall) from updates which (looking at dates) which can be deleted if your machine is stable.