Tomato I am not real sure about but dd-wrt has a couple of examples on their site. In the simple repeater mode you pretty much just check a box and put in the SSID and passwords. Using one of the wireless radios as backhaul to the main router is a lot more tricky and you must edit the iptables entries manually. There is a example of the 2 radio setup someplace on dd-wrt but I can't find it for some reason.
Be aware placement of the repeater device is critical. It must be placed in a location that it gets very good signals from the main router but can still transmit to the remote location. Sometime this is very hard when the cause of the drop off is a wall where the optimum point is in the middle of the wall itself.
If you...