HOWTO Enable SSH and AFP on Apple TV

Jonathan Bare's Guide to installing SSH on the AppleTV:

Step 1

Firstly, copy the sshd binary from your Mac to the AppleTV drive:

cp /usr/sbin/sshd /Volumes/OSBoot/usr/sbin/.

Next, copy the ssh.plist file over, so launchd knows to start sshd on boot:

cp /System/Library/LaunchDaemons/ssh.plist /Volumes/OSBoot/System/Library/LaunchDaemons/ssh.plist

Alternatively, you could use the contents of the file from above to create an ssh.plist file.
Step 2

Unmount the OSBoot and Media volumes, reassemble your Apple TV, and power it on. You need to get the IP address of the Apple TV from the Settings menu, once you know that, open a Terminal window from your Mac (or any OS that has ssh installed) and type:

ssh frontrow@your.apple.tv.ip.address

Press return. Type “yes” when it asks if you want to permanently store the key. Then enter “frontrow” as the password.

You’re in.

Full Tutorial with screenshots on AppleTVHacks.net