Amapi v. 4.15 is free and very powerful. A slightly unusual interface, but one hell of a modeling app. Check out the Amapi Forum for download link and tutes (search for "exercises" and "project" and "conforming" for a start). A good, cheap commercial modeling app is TrueSpace - version 4 is very low-priced these days (www.caligari.com). It's the app of choice for PhilC, shouldn't need any more recommendation than that ;o)