It depends a lot on the way they wrote their code. Since they have a limit on the number of threads (Platinum only supports up to 4 threads, while Pro can do 8), I'll assume that their first engineers weren't very smart about it, and if they weren't very smart I'll assume that it won't quite run at 100%. Most probably the CPUs will spend quite some time waiting for the hard drive. Regardless, get that CPU if you have the money. The day will come that more software will be more thread-safe and more multi-threaded.
Just to add a little experience from the Pro version - it certainly can fully utilise a quad-core, but when rendering, it does depend on the codec you're using, to whether or not it can actually render utilising all four core.
I am not sure if the render target format makes a difference, but VMS 8 will indeed max out all four cores when rendering to mp2 format. I never did see RAM usage exceed 3GB, this is on Vista 64.
4eyes - the number of threads and cores don't have to match. On a single core CPU, you can have more than one thread for rendering. Whether that is beneficial or not is another issue, but you can. Similarly on a Quad-core system you can ask for just one thread, or eight - find the sweet spot for your system's memory, disk and project's codec configuration. My system is still a single core (hyperthreaded system) :(