2-3 times a year on my home pc i decide to do some cleanup. i delete all the junk, disable system restore, and reboot (this removes all old sys restore points). then i run CCleaner followed by ad-aware and then a full defrag. While i dont recommend it for a regular user, if your really that interested you could try disabling system restore so that the files are not locked and then enabling it again once you are done.
i find that very often i forget to turn it back on, but personally i dont use it. i have it turned to the lowest storage setting possible. Hey, im good at what i do, but im not stupid enough to tempt fate.