Haven't tried it yet, but you can give it a shot. This looks to be
focused primarily on architecture, but you might have luck using it for
exteriors too:

ftp://ftp.artifice.com/pub/free/win/

or

the "Free 3D" link at http://www.artifice.com/dw_lite.html

These also looks promising:

http://www.smartdraw.com/specials/la...k.asp?id=15612

http://www.download.com/3000-2130-10023008.html

Good luck. If these aren't what you're looking for, try a google
search.