Possibly you already found this when you googled, but I found out at my small company, they use what I'm told is very inexpensive software called Office Cyber Alert. As I understand it, it allows specific websites to be blocked, which they do to a limited degree, but primarily tracks the PC and online activity including websites visited, how much time, etc. I guess it's more of a precaution to occasionally provide a tool to help support computer use rules and protect the company if anyone is engaging in some shenanigans online. He says it's pretty cool and easy to use.
Sorry -just realized this is an old thread, probably long since resolved.