mental ray is a 3rd party renderer... but anyways you can render particles in maya software renderer (just not all of them). Renderman is a standard and not a renderer. I assume you are talking about prman which wont render the particles stright out of the box but would allow you to do anything you can do with the other renderers. But you would have to write yoru own shaders to be able to do it. Plus you have to come up with the money to buy prman.....

:bandit:
Alan