If you don't wanna waste time developing a ful model, only to ocme up with problems, use SketchUp first.
IM NOT ADVERTISING, JUST HELPING (espech the ppl who may b rubbish at 3D design like me) Am using this program atm Version 4 is free tho you cant export anything, tho u can import .3DS models. I also have the trial version of version 5 Pro, tho i only have 8 hrs to use it in (tho if i run the program, laod my design and export it im sure them 8hrs will last a while

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To find this, just search Google for Sketch Up , theres even a few decent video tutorials to wotch. Have Fun
Check out a design im working on atm. its not brilliant, but it aint half bad. check out a design im working on at
http://forum.thegamecreators.com/?m=forum_view&b=3&t=85965&p=1