Read the last two months of the Terrain Editior forum. Eveythings in there.
Most of the old aircraft (P38 included) are a squeak to work on because of the way the models are put together. Best off sticking to the newer ones that have less bugs.
Theres a file that snips certain stuff out of the object list. shpfilter something or other. The 38 is probably in there.
Gatso