I'm far from being a specialist, but a friend of mine has re-written the rib export plugin that's available here on Highend3d ... You will find it in the plugin or MEL/Scripts section, and it is the RIBExport plugin from Olivier Renouard. It uses the previous plug, but with better poly export (I think it uses the Maya UVs properly). You can try the Maya built-in Rib export as well. I've never tried BMRT myself, but had a look on it when O. Renouard used it, and it seems to work correctly (exepting the very very long render time). As gmask says, it only exports the models and UVs, lights ... For the shaders, you'll have to use wether MTOR or Shadetree, or write your own shaders ... In this last case, I've heard that refering to the two Renderman books existing is of a great help, and being a CG developer might be a prerequisit ... In my case, I'm using MTOR, which friendly-user interface is of a great help when being unable to write a single RIB line 