I was working on a Supremacy/Rebellion Scenario a while back but it never got finished. The units for it are at:
http://www.enixine.dabsol.co.uk/SWScenario.html
My scenario was based on the Lucasarts "RTS" (actually largely TBS) game Supremacy (or Rebellion in US Territories). Land squares are single planets of differing terrain, and the sea squares are space terrain. Starships are like boats, carrying troopers to and from planets. Starfighters are like aircraft and can attack numerous times per turn.
The galaxy is also littered with one-square terrain called Stars, which are impassable terrain because they have diplomatic barbarian units on them with impossibly high ADM ratings. There are no nuclear weapons in the game.
The problem I've encountered for this is primarily that the computer AI handles naval strategy extremely poorly. So it would be an interesting scenario for multiplayer, but the single player game is a bit unchallenging.
If you can manage it, altering the .dll files to put in Star Wars faces to all the tribe leaders is great fun as well! (Jar Jar Binks looms large.)
