nVidia nForce 3 SATA controller does not support NCQ. nForce 4 chipset is the first to support this feature. You can always buy a separate SATA II/NCQ PCI controller, which shouldn't be that expensive.
From the reviews and benchmarks I've read, NCQ is of minor help. I doubt you will notice much improvement in day-to-day tasks. I think we won't see amazing leaps in HDD cache technology until Longhorn ships with it's support of hard drives with some sort of built-in memory controllers, for the lack of a better name. So, I would say save your money for a WD Raptor or technologies with tangible benefits.