Even according to the MRTG page for "supported devices," they mention that the WRT54G is only supported via Wifibox and WW-DRT firmwares.

I tried both today, with no luck -- but it appears that you have to redo your security settings (make a new shared key and/or SSID) because I backed down to the Linksys firmware after testing the others and wasn't able to reconnect until I changed my SSID and key.

So, tomorrow I'm going to test the other firmwares in conjunction with setting new SSID's and keys and see how it goes.