AFAIK, the nVidia IDE driver enable NCQ by default, but as sxr7171 said, enabling NCQ infact hinders performance.
If you want to enable/disable NCQ, go to Device Manager, double click IDE ATA/ATAPI controllers, then select one of the NVidia NForce4 ADMA controllers where your SATA drive is located, select the primary channel tab, and you can select/deselect the "Enable command queeing" box.