Sounds like you are looking for a captive wireless portal solution. Simply Google “captive wireless portal” and that will give you some companies and solutions. Good luck.
There are many ways of doing it, this is my way of doing it.
1) Any wireless AP device [a linksys wrt54gl would be very nice will explain later]
2) a descent pc with 2 network cards.
3) download zonecd from publicIP
another way of doing it.
this is a very nice program which can be installed on a linksys router.
– open mesh
– wifi dog
– Wireless distributed systems.