- First make a backup copy of your xorg.conf.
- Comment out the composite disable option. You don't need to uncomment the enable option; it's enabled by default.
- The "# Removed" options are the things that get changed when you apply new settings through the GUI. It comments out the previous values. It looks like Xinerama was enabled at one point (which probably inserted the Composite Disable option). You can get rid of those if you want.
- Get the setup working first then work on upgrading the drivers if you want.
I think (but I'm not sure)... that Linux Mint uses the same PPAs as Ubuntu. So to get the latest video drivers, you can add the Ubuntu X-swat PPA:
sudo add-apt-repository ppa:ubuntu-x-swat/x-updates
sudo apt-get update
Then go into the Update Manager and there should be a driver update available. (Note: The latest version, 304.something, should be posted within a couple days.)
After the update completes, you'll have to reboot for the new driver to take affect. Don't be surprised if it doesn't reboot though. Sometimes people have problems updating the drivers from the repository. If it boots into a black screen, or hangs on the splash screen, just reboot again and it should work.
(Not to scare you... I just wanted to mention that sometimes the driver updates are hokey.)