At my school, they have an open wireless network set up. If you connect, all ports are blocked except 80 and if you attempt to visit any website, you are automatically redirected to a single site. At this site, you can enter a username and password. When you enter valid credentials, you are given full access to the internet. I want to set this up on my private LAN at home. I have a wireless router and a linux server. I'm assuming I would want to connect my linux server directly to the internet, then share that connection with the router, but where would I go from there? How do I restrict the traffic going through the server and then allow full access to particular clients on the lan? Any advice would be greatly appreciated, thanks.

If it were me, I'd ask the IT department, probably the Network guys, at your school and ask them how they've configured this. I suspect they're using an Enterprise level wireless system that allows this type of configuration via it's software. You may be able to do this with a Linux based server but with my limited UNIIX/Linux skills I wouldn't even be able to begin to figure out how. You may want to try posting this in the Linux/UNIX forum as well.

Hint: internet cafe software. You proxy the wireless connection. Imagine the power if you knew how to internet search