Your problem is in the OS. Windows Vista 64 bit is not yet supported well (many drivers still in beta). Windows XP 64 bit is hard to get nowadays (support has been stable but limited).
Virtually all processors are 64 bit and all other hardware supports this.
As always in 3D graphics, you will need to buy the fastest processor you can afford and with a 64 bit OS you need to buy a motherboard that can support a huge amount of RAM (8 Gbytes minimum) and put a reasonable amount of RAM on it to begin with.