If you don’t have 3DS Max, you can download MR Standalone here to get the DLL’s:
http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=17478798&linkID=9242259
You want to copy:
cudart64_32_7.dll
libiray.dll
libiraymr.dll
To your Maya\bin\ folder.
Make this script a shelf button or something:
http://www.creativecrash.com/maya/downloads/scripts-plugins/c/enjoymentalraystringoptions
It has the settings for enabling iRay properly, Among other things.
And you can get interactive updating by leaving the render window in IPR mode.
Fairly big thread about iRay in Maya here:
http://forums.cgsociety.org/showthread.php?f=7&t=877874
And a guide for what does and doesn’t work right now:
http://forum.mentalimages.com/showthread.php?6584-Maya-2011-and-mental-ray-iray


