I'm currently rendering a sketchup model (exporting a fly-around using the free Xvid MP4 codec), as I write this in VMware's virtual linux machine running firefox inside Window$. This afternoon, I was rendering another sketchup project, while also rendering a Poser animation, while also doing other tasks on this computer. I'm using a quad-core Q6600 with 4GB ram with an nVidia 7600GT GPU. My motherboard is an ASUS P5B. Incidentally, I recently made a system identical to this for a friend except for skipping the 7600GT in favor of a P5 motherboard that includes a GPU, and the cost came to little more than $500, using a case with a very good power supply (not a good idea to buy a cheap PS if you want a stable system). The Q6600 overclocks nicely to 3.05 gHz.
I found this thread after searching for "graphics card," as I was hoping that by upgrading my 7600GT to a 9600GT or 8800GT I could get faster rendering times. Too bad it doesn't work that way - I'm only loading the CPU about 30% at the present time. Renders take soooo long; let's hope the next release of SU will incorporate multi-core rendering. Incidentally, rendering with the Divx codec, which claims to be optimized for 4 cores, does not accelerate rendering times or CPU utilization.