Quad core processor but not terribly different from dual, and rendering speeds up for each core you add in pretty much a linear way.  However, this depends on where the "hard part" of the image is - if you have a lot of "hard part" in the top half of the scene, and a lot of "easy parts" in the other half, then the top half is still going to take a long time to render.  Something to consider though, the Core 2 is just a tremendously quicker processor than the Pentium 4 even with just one core being used (i.e., anything Poser except for rendering).

Poser 6 will not benefit from multiple cores.  Poser 7's renderer will, but no other aspect of Poser 7.  If you wait around for rendering to be done, it can help you a lot to go to a bigger/multi core processor.  If you spend all your time in Preview, it may not help you so much.  On the other hand, you may be able to render at MUCH higher quality than you are used to using, if you went to a bigger/multi core processor (I did).

Think about going with more RAM also, if you decide to pick up that box.

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