Roberta that's a very very nice box - I think though that you could get more hardware for less money, you're paying for the Directron brand name to at least some extent.  Also, I own a Core 2 Extreme qx6700 (a very similar chip in design to your choice but clocked quite as high) and imo, you'd do nearly as well to get an Intel Q6600 for FAR less money.  However if you're prepared to drop the cash for it, the QX6850 is the fastest commercial PC processor in the world.

I'm a little wary of the motherboard and the nVidia NForce chipset.  I own an ASUS P5WDH Deluxe motherboard, which is built around the Intel 975x chipset, and all my apps work.  I'm not saying you need to buy a 975x motherboard, but I have no data on how well the nVidia chipset behaves with any 3D apps.  Probably this is not too much to worry about, but after all you're talking about $4500, so you may want to call your app vendors' tech support and ask them about this motherboard before buying.

4GB downside is not a good place to start.  I can tell you with certainty that in order to upgrade, you will be throwing away 1GB memory modules in order to go up from 4GB, and it is really nice to have 8GB.

2x graphics cards is $500 of waste for 3D applications.  It's a gaming technology that even for gaming is of questionable value.  The application has to be written specifically to make use of the second card, and Poser isn't - 3ds Max isn't - Vue isn't - Maya isn't - Cinema 4D isn't.  That 8800GTX is not a cheap card either, it retails for about $500.  Maybe in the future, render engines will commonly make use of graphics cards to help render, but today they don't (certainly Poser doesn't). 
http://renderfred.free.fr/articles.html

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