BleepingComputer.com: Linksys Repeaters + Macs = Self-assigned Ip Address!?

I have a large network spanning many computers (the users of which share the cost of the connection) and I'm having trouble with my Linksys repeater.
All the PCs on the network connect instantly, but the Macs going off the wireless repeater halfway down the hill are all giving me the same message: "AirPort has a self-assigned IP Address and may not be able to connect to the internet". I've tried restarting the network, renewing the DHCP lease, and a host of other things, and still the things won't connect right!

DETAILS:
Linksys router connected to directional antennae and one repeater sending the signal down the hill to a trailer on the property, whose owner uses said Mac. Terminal pings to the router are successful, so the antennae are not the problem. We've had issues with repeaters and macs before.