Using a Linksys WRT54G or other router is it possible to do the inverse of the "Website blocking by URL Address"? A client would like to set up a PC in their child's room that would only allow her to go to five pre-approved web sites. Everything else would be blocked. Ideally you do this at the router level by client PC's MAC address. You plug in the handful of sites that can be viewed in the router's web interface. All other services would be blocked. Do any of the third party firmware's do this?