Airport Extreme: How to share a hard drive over the guest network? I'm offering my Internet to somebody living in another apartment and used an Airport Express to extend my Airport Extreme signal. Since the Aiport Express only extends the "main" network, the other person is using the main network whereas I'm using the "guest" network myself.

I recently got an external hard drive and connected it to the Airport Extreme's USB port because I want to use Time Machine to automatically backup my MBA. 

However, the hard drive is automatically connecting itself to the "main" network. Is there a way for me to access the hard drive through the "guest" network instead?
The most up-to-date version of AirPort Utility is 6.3.2.

According to this Apple Release Notes of AirPort Utility 6.2, you can extend guest networks as a part of the update.

The most current AirPort Utility is 6.3.2, which is available through software update. I however is able to find 6.3.1 in this Apple Release Notes.

This will solve your problem easily by letting yourself use the main network, and your neighbor using the extended guest network.