If I make a map using this mod, do I need to keep the mod in order for the save to work? I'm hoping to just make a map like Earth, and then play on LAN and it would be easier if my friend didn't need to download the mod as well

As far as I understand, once you save a running game, the save game remembers the mods used, so you would get an error if it was unable to re-load that mod.

yes, but the scanrio is not listed in the modlist of the savegame..

how would the map be generated by other players if only the person hosting the game has the scenario installed?

would only my game map the world as it should, or would thier game do so aswell, even if they dont have the scenaro installed

I think in MP everybody needs the mod, but I'm not sure. I never tested it :s

If you have tested, let me know, I might add MP support later.