the processor option is found when batch rendering, it pops up a window with number of processors to use, but you can check the 'use all available processors' box... it was nice to have when i had my dual pIII up and running.

as far as rendering goes, it's not really a good idea to do much of anything else while it's batch rendering (or just plain old rendering) just because of the fact that maya's utilizing most of the processor. i usually just walk away or start my batch renders right before i go to bed. i also don't leave maya open while i'm batch rendering. i use the command line option after setting my render globals, saving the file, and closing maya.