Attached Link: http://www.exluna.com/products/bmrt/index.html

Renderman is a standard for renders. It was developed from Pixar. Toy Story and Monster Inc. are made with Renderman. There are many implementations of this standard, one of them BMRT is free and good (see link). Another good link is http://www.renderman.org/

Also Poser 4 is already Renderman compliant. You can export your scene into the RIB format. The sad thing is that you have to manually hack this file because the lights are not included and the textures don't work right.

But if P5 has a nice GUI for Renderman it is a big step forward.