Under Ubuntu 11.04/10.10/10.04, launch the Terminal (Ctrl+Alt+T) and run this command to know your current OpenGL and Nvidia driver versions:
glxinfo | grep "OpenGL version"
For Ubuntu 10.04/10.10, you need to install this package from the Terminal before running the command given above:
sudo apt-get install mesa-utils
Here is the outpout I have got:
~$ glxinfo | grep "OpenGL version"
OpenGL version string: 3.3.0 NVIDIA 270.41.19
3.3.0 ---> This is the OpenGL version
270.41.19 ---> This is the NVIDIA driver version currently installed on my system.