If money's no object, quad core should be your starting point and 64 bit no question and then stack it with 8 Gig RAM so when the pro version comes out it can utilize all the RAM available when rendering.
This is my current system which I mainly use with Vue6Inf andPoser 6 and 7

Quad core Q6600 processor
Nvidia 8600GT 256 Meg graphics
8 Gig 800 MHz RAM
Asus P5K-E Mobo
Vista Ultimate 64

This has really stabilized Vue in particular and I can put lots into scenes without anything choking. Even with this though if you put too much in a Poser scene and try to render it in Poser it will choke because Poser can't take advantage of the extra RAM available in 64 bit, Vue can because it's a 64 bit app. With the release of Poser pro that will change!
This is another reason that I render in Vue, I build the scene in Poser with as much as I want and then take it into Vue for rendering!

Injustice will be avenged.
Cofiwch Dryweryn.