are the laptops accessable so you could edit the registry? there are blocks you can add in there to block the sites or if you are in a company you should have a proxy server and you can add the sites in there that you want to block. but this wont stop people from running a different programs that access the site in different ways so be sure to add prot blocking for MSN explorer and I beleive yahoo has something like that too. Also you can check the log files to see what sites are accessed and block the ones you think are Messanger sites.