Providing a Whitelisted Wireless Hotspot?

Ploxis writes "I volunteer some of my day managing a small network (and a ragtag band of computers) for a local nonprofit. I have been asked to set up a second, open, independent wireless network on site that will provide cost-free broadband Internet access to patrons. The catch is that they want to provide access only to a select group of about 25 websites while disallowing everything else. No objectionable sites, no mundane but non-relevant sites such as online banking or YouTube, and no other activities such as P2P or IM. They only want HTTP and HTTPS activity from a set of whitelisted websites." For the rest of Ploxis's question and his intial thoughts on making this happen, read on below. "They'd also like any non-whitelisted URL to be redirected to a 'splash page,' which would just be some HTML providing a list of allowed sites by category. I'd host this page internally on the network. Their primary concerns are liability for access of illegal/objectionable materials and conserving their bandwidth, while still providing access to specific relevant tools online. My initial thought was simply an open wireless router, a set of remarkably restrictive firewall rules, and an in-house server as a custom DNS ... but that's pretty shaky (i.e. anyone specifying their own DNS can still get at whatever they want). I assume they'll need a router with some pretty significant traffic management capabilities as well, but that's not something I've investigated before. Anyone's experiences, recommendations, case studies, or maps of similar networks would be greatly appreciated."