When I tried Mint 12 it did not display properly, I had desktop wallpaper and icons but no panel, and when I opened windows the display degraded to the point where the widgets did not work. Here is my solution.

Boot the live DVD or CD

right click the home folder and select 'open in terminal' - this will give you somewhere to work.

sudo apt-get update

sudo apt-get install nvidia-current

Ctrl-alt-backspace to restart graphical server.

Log in as 'mint' no password, you should now have two panels and a stable graphical environment to work from.

Run the installer until it completes then restart your machine.

Right click desktop and select 'change background'.

Select all settings/additional drivers.

Choose Nvidia version 173, I have tested the recommended 'current version' with and without updates, and windows sometimes appear as silhouettes when maximised, this problem has not occurred since i changed to 173. If you suffer from this problem check this tutorial from time to time as if I get these problems again and solve them I will post the answer here.

The 'enter administrator password' box will appear as a grey shadow, so just type in your password and hit 'enter'

When it has installed restart your machine again as prompted and all should be well.

Hope this helps.