a simple and easy to use 3d modeling program is Metasequoia, i use it, its a really simple program, though unregistered it will only export to its native format (.mqo) exporting to .obj or .3ds is disabled untill a key is brought, but its still good for modeling, there are some freeware and shareware versions available at
http://www.metaseq.net after going in, click on the green tab that says english, and it will go straight to the downloads page.
the freeware can export to all formats, but are less advanced, the shareware need a key but are a bit more robust and adabtable.
hope its usefull to ya all!
the program also uses, you guessed it, python scripting, to help create new plugins, etc...
but there is a Plugins SDK for visual basic or C++, maybe someone will develop an STBC import and export plugin or it, which will allow us to edit the anims and generate new bridges that work ingame aswell. well, thats my two cents.
