If you go to:

http://www.vislab.usyd.edu.au/sidefx/

you can download a "personal" version of Houdini, the software the Rhythm & Hues uses, that was used in parts of Spirderman, and parts of "The Sums of all our Fears"...and the M&Ms characters. Plus, by following the links, you can get tutorials in pdf format.

And if not, you can at least download their propaganda reel:

http://www.vislab.usyd.edu.au/sidefx...Ireelsmall.mov


Oh, yeah...it's a Windows program.

My Best,
-g-