To install, just copy the plugin to /System/Library/CoreServices/Finder.app/Contents/PlugIns on your Apple TV.
After it's in place on the Apple TV, you need to restart Finder (either with killall Finder if you have killall installed, otherwise use ps awx|grep Finder to get the PID and then kill PID.)
FRAppliance 101 - a great introduction to writing plugins.
ericIII from the AwkwardTV crew has created a plugin for the Apple TV that, like Sabertooth’s plugin, hooks into the main Apple TV GUI. However, this one plays videos, and sports a (for now, hardcoded) list of .AVI files that are not located in the Media Library.
ApplianceTest Source Code.