Restricting User Accounts to set of URLs

I’ve got multiple users on the same Win XP machine and I want to restrict where some of them are permitted to use a browser to surf. I don’t want to manage this within browsers but at the user level.

e.g.

A) admin account – unlimited access to any URL
B) permit visiting any from list of 20 URLs (and subdirectories on those domains)
C) permit visiting any from list of 12 URLs (and subdirectories on those domains)

B’s and C’s list may have some overlap, but it’s probably best to treat them independently.

I just uninstalled Norton Internet Security which could do this, but there were many problems outside of this feature requiring getting rid of NIS.