Whew, might try this on the G5...
Safe Boot , (holding Shift key down at bootup), use Disk Utility from there to Repair Permissions, move these files to the Desktop.
/Users/YourUserName/Library/Preferences/ByHost/com.apple.networkConnect.<12 digit number>.plist
/Users/YourUserName/Library/Preferences/com.apple.internetconnect.plist
/Users/YourUserName/Library/Preferences/com.apple.systempreferences.plist
(You'll need to Trash the originals of these following ones since move only copies them)
/Library/Preferences/SystemConfiguration/preferences.plist
/Library/Preferences/SystemConfiguration/com.apple.airport.preferences.plist
/Library/Preferences/com.apple.sharing.firewall.plist
Looks like in 10.5.8 on my G5 that these files cover it...
/Library/Preferences/SystemConfiguration/com.apple.smb.server.plist
/System/Library/LaunchDaemons/com.apple.AppleFileServer.plist
/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist
/Library/Preferences/com.apple.networkConfig.plist
/Users/YourUserName/Library/Preferences/com.apple.systempreferences.plist
Then reboot once more.
PS. Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.