Having had problems installing Mint 12 on my Sony VGN-S5XP with Nvidia GeForce Go 6400 graphics, I thought I'd share my experience. My fix is a variation on the advice given here http://community.linuxmint.com/tutorial/view/691 with some changes based on several days of frustration.
As shown in the other tutorial
Boot the live DVD or CD
right click the home folder and select 'open in terminal' - this will give you somewhere to work.
If you can't see anything when you right click, try Alt-Ctrl-T. This should open a Terminal window from where you continue with typing
sudo apt-get update
sudo apt-get install nvidia-current
Once that has completed use Ctrl-Alt-Del followed by hitting Enter (Not Alt-Ctrl-backspace as described in the other tutorial) to restart the graphical interface. Login with Mint as the user and no password. The interface should now look correct. Now run the installer as normal.
After restarting I had great problems getting the interface to load correctly. I had a screen full of interference and no ability to right or left click on anything. The way round this was to hit Alt-Ctrl-Delete, then Enter to restart the interface, then when it asked for a username, look for the settings icon next to the box for entering your username. It looks like a cog. Select MATE as the interface and put in your username and password which you selected when installing.
This should start up in the Gnome 2 MATE interface and look correct. Now do the same update process as before. open a Terminal window and type
sudo apt-get update
sudo apt-get install nvidia-current
sudo apt-get update
sudo apt-get install nvidia-current
After completing the update, restart the computer and select the first entry 'Gnome' as the interface type before putting in your username and password. It should now start in the Gnome 3 environment as normal. Eh Voila!