Captive Portal on Linksys Router Running DD-WRT

I need a simple Captive Portal (or something similar) application that will run on a Linksys Router (WRT54GL) running a DD-WRT firmware. Users will connect to the wireless router to access the network and try to access the internet. The application should be able to redirect users to a custom html for authentication. In this html users will be ask to input their email, name, cell phone and date of birth. This information must be store on a remote Database (MySql) along with the user MAC address. The clients must be unique, so the captive portal must check if the users already exists (based on their email address). A client can have more than 1 MAC address associated. This are the basic requisites, if you are interested on the project I will send you the full requirements on a pdf.