Of primary importance is the graphics card. There are cards designed for high end gaming, do not go that route. There are cards designed for 3D rendering and display - get one of these. I went with an NVIDIA Quadro 2000 (a mid to high end card at the time with 1gb ram) in July of 2009 and run arcscene as well as other 3D visualizations without trouble. I am sure there are better cards out there now.
Regards,
Jim