I see! I missed that when I looked earlier. If that is the case, then once you enable WDS in the router, you should just have to configure the WRE54G. Are you using the WRE54G "wizard" app or trying to configure manually? Also, I assume you connecting directly to the WRE54G via a ethernet cable, right?
Last, make sure both your WRE54G and the router are in the same network address range (e.g. 192.168.1.X, note the third octet/number).
Good luck!