How do I find my external hard drives that a connected to my Airport extreme with my apple tv?

Hi I am trying to set up our house to be fully networked. We have an airport extreame the network is up and running all the Apple TVs can show photos and music from the ipads and iphones. I can't reach to the external heard drives with the apple tv is it possible to do this? How??

We can't see the printer I connected to the Airport either will it work if I am running it through a hub instead of as the only connection to that USB port?

Thanks in advance for any assistance.

Bruce