Mount external HD connected with USB

Ok basically my setup is…
ATV with take 2
Airport Extreme
Two Macs.
750GB External HD

Basically I want to be able to access the HD from the macs and the ATV. I thought I could mount the HD from the apple tv when its connected to the Airport. But my ATV is take 2 which messes the whole thing up.
Another option is enabling USB then finding the HD on a mac.

What would be the most efficient way to do this?

Cheers

Take a look here:
http://forum.atvflash.com/viewtopic.php?f=12&t=692#p5354

Ok that all seems to be working now. Cheers

Is there any way that I can find the external HDD that is connected to the ATV on my mac? I tried using Cyberduck but didn’t really know where to start