Can preferred networks be reset?

Try this:

System Preferences ⇒ Network ⇒ Adanced ⇒ Check box for 'remember networks this computer has joined'

Is your network in the list of Preferred Networks on that page?

In the Preference Pane, try deleting it ("-"), hit the Apply Button, then Add it back ("+"), and Apply

My list of preferred networks is greyed out (can't + or - them) when I go to the advanced tab under network prefs. Anyone know how to erase them and start over?

You are maybe not authenticated as an administrator. You have to go one step back to the network preferences window and click on the lock to open it.

oh gosh, of course. thank you.

You could also try deleting the keychain file and and re-connecting to network.

Please try changing your router wireless security encryption from WEP 64bits to WEP 128 bits (HEX), and I believe everything should works. I think the 10.6.5 OS update create some wireless logging on problem, and so it will only recognize wireless SSID broadcasting WEP 128bits or WPA encrypted signals. The rest of the SSID will not be recognize and so all your preferred network will not show up.