Ok.. first of all, what is this video card and what kernel module is loaded:
$ lspci -k | grep -A 2 -i "VGA"
02:00.0 VGA compatible controller: nVidia Corporation NV41 [GeForce 6800 GS] (rev a2)
Kernel driver in use: nvidia
Kernel modules: nvidia, nouveau, nvidiafb
So I do have nVidia graphics card with loaded kernel module - "nvidia".
Let's see more about this driver, but search for the "version":
$ modinfo nvidia | grep version
Although you could just read a full output if ".. | grep version" returns no result:
$ modinfo nvidia