I've noticed a lot of open wireless access points will associate but won't forward your traffic until you attempt a web connection. This attempt is redirected to a TOU page. If I want to do something similar, what's the "best" way to set this up? I assume low-end WAPs (like the ubiquitous Linksys WRT54G) can't support this directly, so I'd set the WAP as a router (rather than gateway) and then use some kind of software on a Linux box to handle this?
Load ddWRT or OpenWRT firmware on it; they both have captive portal support (which is what you're looking for). The process isn't super easy, but there are plenty of directions on both websites.