Selective access to websites

Hello, I am trying to figure out if there a way of blocking access to a social networking website, but I don't want to block all users, I know I can make an entry in the hosts file to block access but I want certain people to still have access, Would making and entry in there hosts file (they are running windows) and leaving the hosts file on my gateway machine (slackware) blocked work? any help would be really appreciated, thanks guys (and girls if applicable )