Can iOS 4 connect automatically to a closed network with a hidden SSID?
Note -- I haven't tested this or worked with a similar configuration *


It isn't clear from your description -- does the iPod auto connect to the "Guest" network?

If it does, in the Wi-Fi settings I would (in the WiFi settings) turn "Ask to Join Networks" off then tell the machine to forget the "Guest" network, then connect to the hidden network again and then sleep the device and see if it reconnects to the hidden network.

Or -- Go to Settings then General then Reset and then Reset Network Settings, then power off and power on the device, then reconnect to the hidden network.

Or -- you could also try Apple's iPhone Configuration Utility, which allows you to set profiles for iOS devices. I haven't messed with this at all, but some folks have mentioned it as a fix.