Holomatix recently announced the availability of SprayTrace for Maya which creates an instant preview of a Maya MentalRay scene by providing real-time feedback on shaders, textures lighting and camera adjustments without any special hardware requirements. Check out the page that Holomatrix has created for SprayTrace for Maya for Instant Mental Ray Previews here.
SprayTrace has no special graphics card requirements, instead utilising CPU power to deliver its preview. Even modest 3D workstations will enjoy great performance. The only other requirements are Windows 64-bit and Autodesk Maya (versions 8.5, 2008 to 2012 supported).