MAC address controls are only possible for hosts on the same network ("broadcast domain"). Any remote host that has to be routed to you, such as over the Internet, will appear to come from the MAC address of your router, and so can't be subject to MAC address controls.
That's why you see MAC address controls used with wireless access points, for example; by definition a wireless client is going to be "physically" connected to the access point without any intervening router.
I assume from your description that the "trusted members" are probably remote users, so MAC filtering won't work for you. Given your stated ultimate goal, you may want to consider two-factor authentication of some sort. Giving out SecurID or other hardware tokens might be overkill, but perhaps client SSL certificates would provide the combination of security and convenience for something on the order of a "local gaming website". Setting up client certs has an initial (time, energy) cost, but once you've handed them out and people have installed them, it provides stronger assurance that the right people are logging in with little to no added inconvenience for everyday use.
