You should use your package manager to install the Nvidia drivers because when an update comes down the pipe it makes it easier to upgrade the kernel and still keep your nvidia driver, or even get nvidia driver updates automatically.

If you have the other nvidia driver installed you will need to manually uninstall it. At least in my experience that is the most successful method. Those details are outlined in the read me file that came with the driver.

If you want to use the tested drivers that work well under Ubuntu then run this command

sudo apt-get install nvidia-current-updates

That should do it. If it is working successfully you should have an Nvidia control panel you can locate that in the dash.

It should give you your nvidia system temperature and other facts about your card.

hope this helps.