My father in law is an architect and is about to retire his old single core Pentium with 2GB RAM and a 256 NVdia graphics card because AutoCad Arcitecture 2009 & Revit Architecture 2009 run slow on the machine. Especially the rendering seems to take a long, long time.
Since I am the one looking for a new one for him I am wondering what to get (since I have zero experience with the program).

Is it better to get a really nice fast dual core with 4GB ram and a better graphics card (like a 512 one) and a nice 24 or 30 inch flat screen or a dual core with a little less graphic card, same memory, smaller monitor. Both come out to about the same price. I don't know if the program even takes advantage of the quad core architecture or if memory, fast HD and a good graphic's card are as important.
Any help would be appreciated.