If Inventor is going the way of C3D, then you probably want Vista x64 boxes. (Too bad you can't wait for Win7.)
And with Vista x64, there's not much reason for a Quadro FX1700. You could get GeForce 9600 GTs or similar PCIe2.0 card instead.
And with Vista x64, you'd be better going with more RAM. It's cheap. 6GB is optimal for many, but you could go down to 4GB. I wouldn't go any lower.
Also, with Vista x64, you really don't want a measly 80GB hard drive. But 500GB vertical-write (i.e., faster than a 10K WD Raptor) drives are less than $80 now.