MacMini WiFi Range

I switched my old PowerMac G5 (1.6 GHz, OSX10.5.8, 1.5GB ram) containing a 3rd party wireless card and Ralink software over to a 4 yr. old MacMini (OSX10.7.x) (system is used at a lake cottage). The WiFi is antenna based and via a shared non-Apple router at my neighbor's home about 80 ft. away. When I installed the Mini the WiFi connection was almost impossible to maintain and I could not get an older (first gen) Airport Express to join the existing network. Can anyone please suggest possible options; would replacing the router with an Airport Extreme work?