Now Brycetalk, your question. 

I have a quad, 6 Gigabyte of DDR3 RAM computer with Vista 64/32 bit (has both modes).

Does it use more RAM, yep Vista must have 1Gigbyte, and the latest versions of Carrara, Poser etc also use around a Gigabyte of RAM, does it use RAM above 3Gigabyte--it depends on the software and since mine are all 32Bit, the ceiling is around 3 Gigabyte.

Now does Carrara render faster than with one CPU, you betcha, four times as fast-there are four boxes rendering at the same time, when one CPU finishes its rendering, it creates another box and begins again.  That's Carrara 5 Pro by the way. 

By the way you don't have to decide whether to run your software in 64 or 32 bit mode, Vista figures out the mode for you upon installing-In fact Vista will not allow you to run a 32 bit software program in 64 bit mode if you are thinking about utilizing all your GigaBytes. 

Jan