You want as fast a CPU as you can get.  I always use AMD CPUs.  They tend to be faster and a lot less expensive.  Also get as much RAM as you can possibly afford (up to the max supported by your motherboard.)  And make sure it is the fastest your MB can handle.  Oh yeh.  A multicore CPU really does speed things up quite a bit.  AMD has up to 6 cores now on their Phenom II 64Bit chips.  As for the graphics card.  That has nothing to do with rendering.  But you always want to get a decent card.  I use a Sapphire ATI 4870X2 HD 2GB PCIE card and it looks great. 

I use an MSI 790FX-GD70 Motherboard with a Phenom II X4 X64 CPU, and a full 8GB of system memory (Corsair).  A system like mine is not top of the line, but it is a very respectable rig for 3D work.  And you could probably put one like mine together for a pretty low price now.

Hope this helps.

Quote - Which is more critical for rendering in Carrara, the graphics card or the CPU/ram? I'm going to be building a modestly priced computer - does anyone have any card recommendations. Will probably get 4 to 8 GB ram and Win 7 64 bit, upgrading to C8 when available.

Thanks,
Mike