Fast wireless adapter that can use an external antenna?

We have a dish set up on our roof, something like 18dbi gain, and on top of that it has a powered amplifier ("injector") hooked inline with it, so it should have a huge range. For the longest time, it was hooked to an Avaya Wireless World Card Silver 11mb/s notebook card (adapted into a desktop pc) that used WEP to connect to our ISP's tower several miles away. Well something isn't working with that card, and i was wondering if i hooked a more generic card to it that could scan everything and pick up on stuff like the free public WIFI networks in town (just another mile or two past the tower) then it would fix our reliance on the ISP. So i've been looking, but while i don't see any wireless-n cards out there yet that allow use of an external antenna (we can adapt connectors), i'd settle for a good wireless-g adapter, but it has to be something that i can hook this huge antenna up to.