DNS URL filtering Linux Server

Hello I am looking to create a service similar to open DNS please go to [login to view URL] which provides url filtering through DNS. I am wishing to block various categories of urls such as porn, torrent sites, p2p etc etc. I am presuming I could do this with dans guardian and black lists from [login to view URL], but you may tell me other wise. When a user requests a page that is blocked they will recive an adminstration page telling them the request has been blocked, I would also like a by pass access code as well. In short I have several wifi locations, I want to make a dns alteration within the relevent routers, when clients are surfing and try to access banned sites,the request us checked by our main online server, if in the blacklist they receive an admin screen. I will need a gui of some sort so I can add individual offices as they are all seperate, and each office will be filtered for different categories. Please note I do not need a proxy, I need to allow or disallow their request by our main server, their Internet surfing is done locally not on our server it is acting purely as a yes or no filter 1) DNS url filtering simialr to open DNS 2) Abilty to filter by category per office / location 3) Abilty to add locations quickly and easily 4) Custom admin block screen 5) Override access control password 6) Log files or stats per office IP location 7) Admin GUI I will need the service to be as fast as possible as I do not want their surfing slowed down, so any reccomendation I will listen to. Only skilled Linux users on this job please Please note I am not a new employer I have nearly 50 jobs on an alternative site with a 10 record Thanks Paul