The agent is indeed configurable from sharing prefs.
It looks like they've changed things around since the last time I used it. The controller looks like its now built into OS X Server, whereas client, controller and agent all used to be installed and run from the same app for Panther and Jaguar.
You need the public beta installer. Or a copy of Server (I read a page reporting that you could download the Server combo update and install it using Pacifist. Worth a try.)
I'll hunt around and see if I've got the beta installer knocking about.