Once you got nvidia driver working, for gaming you want to add the following to your xorg.conf:
In Section Screen:
Option "RenderAccel" "True"
Option "NoRenderExtension" "False"
Option "NoFlip" "False"
Option "UseEdid" "True"
Option "NvAGP" "1"
If your motherboard has AGP, add to /boot/device.hints:
hint.agp.0.disabled="1"
and reboot.
Alternatively, install /usr/ports/x11/nvidia-xconfig and read through the manpage. It can update your xorg.conf with driver settings specific to nvidia, at the right spot.