After following the instructions on the nVidia site for changes to the XF86Config-4 (/etc/X11 I think is where it is on Redhat) make the following change:
In the Device section that you would have just changed nv to nvidia add this line:
Option "NvAGP" "1"
That should solve your problem for the vid card settings. Assuming you have set up X-Windows properly for your system (can't recall the x-win config command).