Hi,
Would Gmax (freeware from Discreet) and a graphics editor like PhotoShop or PaintShop Pro support most of the model and texture formats required for a complete model? I've built scenery for Flight Simulator 2004, and I think all you'd need is the details on formats, dymanics or simply a conversion tool from the developers to drop it right into the sim.
I don't know how much has been put into supporting "add-ons" for this sim, but whether the developers go with an "add-on Library" or just pick the best of the uploads and include them in the next update, either would be fine with me.
Yours,
P.S. With the introduction of FSX, even Micro$oft is going the way of "*.dds" texture formats. What format are the models rendered in?