CPU usage when rendering

hi there from sunny south africa, happy new year all around.

what can i do to have all my macbook pro's cores run at the max when rendering? currently only two of the cores seem to be running full out while the other two are pretty much idle (see attach screen shot of the OS activity monitor, it was taken during a long rendering session).

am i correct in assuming that my rendering will go a whole lot quicker if all the cores are maxed, like they are when running heavy compression through compressor, and how can i go about activating the idle cores (i have already unchecked the "automatic graphic switching" option in the 'energy saver' preference window in the OS settings)?

regards

t