Lord Parkin
aka emperor
In the Conquests editor, press Spacebar and select the civ you want to place units for. Then in the tool bar up the top, two new icons will become available (hover over them with the mouse to find them). If you look carefully, you'll see a button for "adding units" and a button for "adding cities". Click them, and do as you please. If you want to place units/cities for a different civ, just press Spacebar again. Once you're all done, save the map as a Scenario, load it up in the game under "Load Scenario" or "Civ-Content"... and enjoy! 
