So I have been scouring the interwebs and I have come across a few programs that would allow us to run a walled garden I believe wifidog is the best choice so far. I've come up with one other program which I'm still reading into. By the way this is Wikipedia's definition of a walled garden. And this is more specific definition of what I plan on doing.
So the way it would work is you would place a machine running Ubuntu with wifidog between the wireless AP and the rest of the network. When a user first opens there web browser and attempts to access a website they will be sent to a splash page that, for our purposes, would ask for a username and password. One more thing, you can use that Linksys router and flash it with wifidog so you don't need to set up a machine but you still need a separate server for authentication.
That's all for now.