My apologies, I did not realize there was a folder called AppData in the Sins directory. The folder I am talking about you can find here (credit to Harpo for this explanation).
assuming you have sins 1.191/entrenchment 1.051/diplomacy 1.011, the galaxy forge maps NEED to be placed here for xp
C:\Documents and Settings\'user name'\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\GalaxyForge
or for vista/windows 7
C:\Users\'user name'\AppData\Local\Ironclad Games\Sins of a Solar Empire\GalaxyForge.
for sins 1.15/entrenchment 1.00 and earlier, the correct location IS the program files \galaxy folder, and you also NEED to edit the entrenchment's galaxy.manifest to include the maps and also the total count of maps
NOTE the first two folders after the 'user name' are hidden , so to see them you must first click on 'tools' then 'folder options', then 'view', then click on 'show hidden files& folders' then click ok, then you will be able to browse your want to the folder. I suggest when you find the folder that you create a shortcut to it on the desktop
And yes, stardock/ironclad people do check the technical forums, but I'm not sure if they'd help with a GalaxyForge problem as that is just a bonus feature Ironclad made on their own free time.
Edit: Hopefully the German path names are similar enough to the English ones to find it.