3DS Max is cool, but as 40hz pointed out, very expensive.
For a free alternative, have you taken a look at
Blender (also mentioned by 40hz)? Its interface is way different than most CAD-like programs, but once you follow some video tutorials and get a hang for how it works, you can do quite a bit with it.
I suppose that if you're using it for CAD purposes, it may not be suitable for that. I'm not sure since I don't do any design. I've just played around with a few 3D modeling programs for the fun of it.