Lightwave 3d and 3d Studio Max are the best programs for creating 3d models however they aren't free (nor are they cheap, I could buy a new computer for the price these things go for!). However, since both are very popular, a sufficient search could provide you with a watered down copy on the net. I think there's a demo version to Lightwave... I know that 3d Studio Max has a free version that's watered down, though if you know where to get a copy of the real deal, don't hesitate.
You want proof of their capabilities? Just look at Space: Above & Beyond, Babylon 5, Star Trek, Star Wars and all those other fancy sci-fi shows... They have each used at least Lightwave or 3d Studio Max, or both. A great accompanying 2d graphics program is Photoshop, though in my view, Paint Shop Pro is almost as good and worth mentioning. You'll need such a program if you intend to do the textures yourself.
Learning to use these however is another question entirely, they are not like Build.exe that came with Duke-3d, you will need to seek out tutorials on the net or from friends who know how to use those programs, or if you want to waste time, try learning everything yourself (though that may take a few years).
All this comes from a Windows user so be assured that everything I said here is based on Windows, the programs each work on Windows 95/98, 2k, Me, NT, XP so there shouldn't be any problems.
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