The software I used was Mr. Planet V2. It has a pretty good interface as far as I remember, but it wasn't super stable and the model you use can't be too complicated. Here's the link:
http://planet.urv.es/planetrv/ It looks like there might be a newer version, I'm not sure what's different about the "castle" and "lite" versions.
Some stuff is in Spanish, and the English manuals if I remember are just translated, so it may take some figuring out to make it work. If you can't make it work let me know and I'll see if I can help!