Ihave been a Vectorworks 10 user for about 3 years and soon will be upgrading to version 11, it is a fantastic program. I have been using it on a 700 iMac that is almost 3 years old as well and its performance has been fine. However, as you begin to work on larger projects, render images, QTVR, and movies, the system becomes a handicap. Drawing lines and arcs doesn't take much processing power, but if you intend on using the built in rendering engine you NEED to upgrade. Every time I adjust a light source or alter the mapping of a material, I choose to see the changes and waste valuable time waiting for the photo to render. The newer versions of Vectorworks, 10 &11, take advantage of the G5 and dual processors. If you are serious about CAD and want to take advantage of Vectorworks or Archicad 3D and rendering capeabilities, upgrade to a new iMac or Powermac. If you just want to do typical CAD tasks like drawing simple lines and shapes, the choice is yours.