ArchiCad North America has an online presentation called "AC Dream Machine". You need to be a subscriber (I think) to see it. Look
here.
Basically buy lots of memory (8GB), use professional video cards with 512 MB dedicated memory (more video memory is usually a waste of money), fast-very-fast hard drives, SAS type at 15,000 rpm, true quad core (not core duo) i7 or better with high Hertz speed. Oh yeah, large monitor at 1600x1200 resolution min. In addition to that make sure the video card supports OpenGL 2 or better and DirectX10, not hard these days.
Think about SSD drives or look
here for ramdisks.
Snap