If an application is single-threaded, as Poser is most of the time (except for Poser 7, and only during rendering), then it will only take advantage of one core.  However Poser 7's Firefly renderer, and many bigger applications' render engines, will run on multiple cores, so rendering can be much faster.  Basically the work is divided up into multiple threads, and each of them runs on a separate core (effectively a separate processor really).

For interactive applications, like using Poser in Preview mode (where you do all the setup work before rendering) or pretty much any other desktop-type task like word processing or spreadsheet, you will see little difference, because typically you're waiting on the user rather than on a busy processor.  Going with multiple cores will often be a great benefit when you're doing large, complex renders - typically, for well-designed render engines (which Poser 7, sadly, is not), this means each core = nearly a 100% increase from the base speed 1 core would run the render at.  Some benchmarks:

http://www.extremetech.com/article2/0,1697,2050007,00.asp
http://www.anandtech.com/showdoc.aspx?i=2866&p=13
http://www.hothardware.com/articles/Intel_Core_2_Extreme_QX6700__QuadCore_Assault/?page=10

Ignore game benchmarks, and "CPUMark" statistics, unless you value game performance more highly than render time - they have nothing at all to do with the render benchmarks.  Also look out for the "Cinebench 1CPU" benchmark - because it actually runs in one thread, and only touches one processor, so it's not a very useful statistic when it comes to multi-threaded apps.

Check your product literature to see whether a given product is multi-threaded or not.

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