Back to the original question,  I just recently purchased a quad with 6Gigabytes of RAM.  I'm still using Poser 5 and to may surprise, all four cpus take a part in rendering the scene and it appears about 3 or  4 times faster than a single 2.0 Gigahertz CPU.  Other software that appears to take advantage of all four are Vue 5,  Carrara 5 Pro, and I think Terragen 2 Preview.  Jan