Hmm just did a little test. I replaced a .tga file for one of the maps with another one i made myself.

The preview picture is taken from the .tga file itself (and thus wrong) but the player locations + supply stashes/oil derricks are taken from the .map file itself. Hmm, makes me even more curious as to how generals is using those files.

Olaf, could you check if the map uses the big compression for me ? or point me to your big extraction routines ?