Oh yeh.  Even though you have a 64 Bit processor, you will still be running it as a 32Bit unless you run the 64Bit version of Vista or XP.  If you get Vista Ultimate in a retail box, it includes both versions of Vista.  If you want to go Vista, I highly recommend the ultimate package and be super careful about what PC you get.  A lot of them say vista ready, but can only run it in it's most basic stripped down mode.  I am also not sure on how well C6 or C5 will work under a 64Bit OS.  There is supposed to be a compatability mode in the 64Bit versions, but I have never used it.  Another conosole.  If you are running a 32Bit version of the OS, your system can only see a maximum total of 4GB of RAM.  In other words, if you have a 512MB video card, you will only be able to use 3.5GB of RAM.  This is a limit of the 32Bit hardware and software architecture and there is no way around it.  If you run 64Bit, the limit does not apply.