Dual-Core 2, no question.  As you research this more it will become obvious.  Forget about what a consumer program such as Poser is said to run best with.  No program (or game) will be poorer for having a second processor available for handling the forty odd other things going on in the background.  While the Duo Core 2 (and new Xeon chips) will run all 32-bit applications they are of course 64-bit, allowing for huge leaps in memory usage far beyond the 4GB threshold (2GB per application) of 32-bit processors.  All applications (and games) which rely on floating point calculations will of course be greatly improved.  The Core 2 Duo series use 1033MHz front side buses with 4MB of shared L2 cache per processor, very nifty. 

The new Mac Pro uses two of the new Dual-Core Intel Xeon processors (up to 3GHz) each with a 1333MHz FSB.  Very impressive.