Experimental drivers no longer visible in "Additional Drivers" menu, how can I manually install them?

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http://askubuntu.com – I just reinstalled Ubuntu and immediately after it was done, it showed me the "Additional Drivers" menu and it listed a bunch of experimental NVIDIA drivers. I did not install them and closed the window. Now, I went back to go to install them and none of them are listed and there's only one that reads "ATI/AMD proprietary FGLRX graphics driver". How can I install an experimental driver if it's not listed there? (HowTos)