Pretty sure it can, i'm running vista 64 on a core 2 duo 6600, if I remember rightly all the core 2 family are 64 bit (other than notebook versions), you may ahve to check the MB to see if thats capable, but it should be, you may also need to find how to change the chipset in the BIOS to see more than 4 gig of RAM if you go that route.

Mastone I think Z is multicore/thread supported, you can run a test in the preferences and enable it or switch it off there.

I doubt it will be GPU accelerated, the whole GPU acceleration is a bit in the air at the moment, theres no real standards between AMD or Nvidia, it's more on the researchy side at the mo though I think it will come to the forefront very soon, also all of Z's coding based on the CPU and the RAM, though there could be room to port some over the the GPU using CUDA, but that mean it will only take advantage of cirtian Nvidia GFX cards.

I think that it will probably go up the route of utalising the CPU and the RAM on high core and RAM systems, I dont feel that 3.1 is slow anyway so not too sure where a major advantage of GPU would come in at the moment, though as a lot of things I could be wrong, only time will tell.