Accessing ATV over internet

Considering my ATV is turned on all day, connected to the internet at home, plugged into my external HD full of my media, is there a way that i can sit at my desk at work, log into the Apple TV and retrieve some of those files over the internet?
Or at least look at the files to see what is on there?

You should be able to just open up port 22 in your router to the AppleTV IP, and then SSH to it using your WAN IP.

From a security perspective, you need to consider the risks of opening up port 22 to the internet though, IP scanners will find it, and start pounding it to try and get in (bruteforce and other).

A good way to thwart bruteforce attacks are denyHosts: http://denyhosts.sourceforge.net/faq.html#1_16, or you can just block everything but your work IP in the hosts.deny file.