Routing via (from) webinterface

Hi all,

How can I limit the lan traffic to selected IP (or MAC?) and redirect
the traffic depending on rights (allowed|not allowed) let's say,
written in a file or in a mysql table ?
I have an web interface written in PHP that will set the mysql database
or write a file, or even lunch the command that will set the *rules*.
I want, for example, set a computer to being allowed to use the xDSL
connection and a second computer allowed to use also the fiber optic.
The two Internet connection are all installed on the router, that would
route each host (via mac or IP or both) via the allowed and active
connection selected (via web interface).
I'm trying to understand which step whould I take in order to make such
a system, provided I have the gui, I'm ok with shell scripting and i
have some skills in networking ?

Thanks for all kind of suggestion and information!

Lawrence