Having finaly gotten, after running a ad-hoc wifi network since 1999 or so, a access point which it's easier to associate with than my old ad-hoc network I've decided to implement some security. The AP can do all sorts of security, including the simple and non-intrusive kind: mac filtering. But I have a geniune self built Linux firewall, so I wanted to do something more interesting: Build a sandbox for visitors.
The idea is, and this is not a new idea, I've read about this numerous times around the web. ... The idea is that if a foreign computer tries to use my Internet connection it will be directed to a web page explaining that I cannot allow this. It may be interesting to extend this, so that if they promise to be good they can use limited bandwidth on port 80 and 443.
The iptables-HOWTO is quite simplistic. The TransparentProxy HOWTO offers some hopes as to how to hijack and redirect connections: Transparent Proxy to a Remote Box. Like a irresponsible home user I've stuffed my firewall with all sorts of interesting stuff, like a web server. So I'll be sending all connections from forreign computers to the Apache on the firewall.
A virtual server on the Apache is needed that always shows the same page, no matter what page is requested.