okay, once you have your galaxy map done that you've made with the Galaxy Forge, save them where ever you want.
THEN, drop them into the (for Vista users)- C:\Users\[username]\AppData\Local\Ironclad Games\Sins of a Solar Empire\Galaxy Forge directory.
If your running XP, it should be a variation of the above directory. For Vista, AppData is a hidden folder.
EDIT: almost forgot this part. You could also just save right into the directory if GF allows you to do so.