The beta-v24 version of the DD-WRT firmware has a new feature that allows it to function as a standalone range expander. This is similar to the functionality provided by a wireless distribution system (WDS) network configuration, but unlike traditional WDS, the repeater router emulates a standard client connection to the parent router. This eliminates the need to have two DD-WRT supported routers, running the same firmware, both set up specially for this purpose.
Simply put, you can configure a single repeater appliance and it will work in conjunction with the wireless router you normaly use at your home or office, regardless of the primary router’s model or firmware. There’s even an “AutoAP” option, which will allow your repeater to automatically monitor and connect to the access point with the strongest signal.
Complete instructions for getting this set up are available at the DD-WRT forums – Link.