Okay, I think I figured it out:
[*]Download and unzip the zip file from http://code.google.com/p/unraid-simplefeatures/downloads/list
[*]Copy the simpleFeatures.core.webGUI-X.X.X-noarch-1.plg to your unRaid server in to /boot/config/plugins (create that plugins directory if you haven't already)
[*]Reboot OR run installplg simpleFeatures.core.webGUI-X.X.X-noarch-1.plg
That will install the core webGUI stuff. If you want something else (like the webserver), then follow the above instructions, but install the appropriate PLG file.
Thanks~!