you should look for unit sprites on the forum, someone has a DB with the sprites of all units from the game (till a certain patch). If you can't find it I could mail it to you but it should be on the forum somewhere, since that is where I got it too

, maybe in one of the stickied threads or something.
PS for gems I'd probably just focus on the 2 main paths of the nation, helps to give the nation identity.
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Want a blend of
fantasy and
sci-fi? Try the total conversion
Dominions 3000 mod with a new and fully modded solar system map.
Dragons wanted? Try the
Dragons, Magic Incarnate nation.
New and different undead nation? Try
Souls of Shiar. Including new powerfull holy magic.
In for a whole new sort of game? Then try my scenario map
Gang Wars.