My PowerBook G4 OS X 10.4.11 is not connecting through WiFi at home. I’m using actiontec. WiFi signal is locked. It works through LAN cable and the Airport works at McDonald’s.
First I suggest to find out which Wireless standard your AirPort card supports. Open System Profiler and go to "Network > AirPort card".
I don't have an older system at hand but the entry should be called "PHY modes" and there the value should be something like "802.11 b/g".
Next make sure that your actiontec Router/AP supports such devices. For example it shouldn't be set to "G-only" mode or similar, also it has to be 2,4GHz because the old AirPort cards do not support 5GHz Wi-Fi.
I also suggest to set the wireless encryption to either WPA or WEP (first one being the better choice) because most older Macs do not support the WPA2 standard.