you dont need them but it will be faster, what they are saying is that when you are using maya you will only be using one CPU at any time. Id spend the money on the graphics card and more RAM unless you are going to be rendering massive scenes. To be honest a dual is probably overkill unless you really really need it. A single CPU will be fine. I use a P3 700Mhz with 256mbs RAM at home and it's fine for what I do there (I use a 2.4 Ghz with a gig of RAM at work and I dont even need that much power).

Alan