What you are looking for is parental control software
What you are talking about is File and Printer Sharing with XP.
OR if you have Vista just take out the XP and put Vista in the google search box. It sounds to me like you have it set up, the thing these guides never tell you'll need an account on all the PCs OR just turn on the guest account.
The reason I said what you are looking for is the parental controls is, with file/print sharing you can get into the files to see where they have gone BUT the parental controls have the power to limit where they can go in the first place =) And good on ya for caring enough to look into this sort of thing.