Basically Pixar Renderman (PRMan) or Renderman-Compliant renderers imports the shaders, the textures, the models, the particles (etc. etc.) and physically draws the frames.

Maya Software and Mental Ray will probably get good enough effects for you -- so you probably shouldn't need to bother :p Sure you may see some enhancements but honestly what's the point.

Another substitute which is coming around is nVidia's Gelato -- the reason why I mention it is because its designed for QuadroFX+ videocards so it SHOULD do pixar-like effects a LOT quicker (all hardware rendered)