Can't install Gallery under Geeklog!

I can't see how this works as a plugin, can someone give me a quick idots guide to installing it. I've already got one working under PHPNuke, so I'm not a complete novice (no need to be gentle :- )

I'm using gentoo linux, and I'm trying to install 1.4.1 of the geeklog gallery modification. Unfortunately, there's no documentation