In order to setup the official Nvidia drivers, you'll need to add the non-free repository to your list of installation sources.
The best place to pick up URPMI sources is EasyURPMI at *easyurpmi.zarb.org/ . Select the mirror you want then check everything except the "backports" options (unless you don't mind running bleeding edge software).
Make sure you run the command "urpmi.removemedia -a" before running the commands it gives you to copy and paste.
To run the commands you'll need to hit Menu -> Tools -> Konsole, and once loaded, type "su" (without quotes) and enter your root user password. Then just run the command above, and copy and paste the commands it gives you from EasyURPMI. (Hint: In Konsole, you have to use Shift+Insert to paste text you've copied.)
Once you have those setup, you'll need to make sure the following packages are installed:
dkms-nvidia-current
kernel-devel-desktop586-latest (or kernel-devel-desktop-latest if you have the high-end kernel)
x11-driver-video-nvidia-current
As long as those are installed, you should be able to use the Mandriva Control Center (Configure your Computer), to setup the system to use those drivers. (Look in Hardware tab -> Set up the graphical server). After it's all said and done, reboot the system to have everything take affect, and you should be set.
Source: Official Mandriva Forum