A 32 bit OS can address up to 4GB of ram, it's simple math.
Windows due to it's design reserves part of the ram for other than user program use.
A 64 OS can address up to 16 Exabytes, Windows 64 bit OSes limit this to 16 Terabytes.
Have fun with that overpriced Nehalem configuration, I will wait until it drops to less than a third of what you will pay for it.
OCZ is good, I have been using G Skill with out troubles.