I have a 24 core MacPro... I have to physically limit the game to just 15 cores or else it will crash at boot. So, no it's not limited to four cores.

64bit addressing on Windows under Direct3D 9 is probably slightly more demandng than 32 bit addressing, as D3D9 requires a context switch between each opteration. BTW, the physical RAM limit in WIndows is 4GB. Though it can address up to 64GB. And each user process can use 4GB of that. 32GB is not limited to 2GB. Windows XP limits the usermode to 2GB, and the kernel mode to the other 2GB. Vista/7 I beleive increase it to 3GB for the user partition.

If you have enough RAM (like 8GB+) the game will take advantage of Windows disk cache. This will automatically cache the files on the HDD in RAM for quicker access. So there isn't much need for an SSD.