Just what it says,it removes any left over rubbish that other programes leave on your comp.
There are four options ,
Temp files,which is usually fairly large.
Temp internet files again fairly large.
Cookies,someone watching what your doing.
Recent files,what youve been looking at/history.
Another tip, if you use vista and you delete various progs that you've D/L,music or whatever,write the name of what you've deleted in the search bar bottom left and you'll find some are still there ???
right click on it and delete.
MAV. I don't know where you are going wrong mate.It's working fine for me.
Lindsay.