You use the sh command to run a file ending in .run
e.g. sh filename.run
That assumes you are able to at least get into text mode to see what you're doing.
Hitting CTRL-ALT_F2 (possibly repeadedly) should get you a usable text mode screen and bring up the text mode login if you're not already there, but instead, staring at a blank screen.
Assuming you downloaded the .run file from Nvidia for your 8800xx video card, you'll need to have installed several development programs, such as gcc, that the installer package will need. If they aren't already installed, the run script will ask if you want the installer to go online and and fetch them. If you reply yes to that, you'll need to have a working internet connection at the time.
If all the above proves successful for you, once the installer finishes, you'll reboot, this time with a working graphical interface. If it reboots with a text mode loging screen, login then give the startx command to bring up X.
I went through a similar situation when installing, first, FC5, then FC6 with my GeForce 6800GS card. But instead of having a blank black screen in graphical mode, I had garbled video. The native 'nv' drivers used in X just won't work with some Nvidia cards, but once you get the nvidia drivers installed OK, life should be better.