If all you are doing is installing an add-in video card all you should really need to do is install the card, plug your monitor into the new video card and boot up the computer.. Once up just install the current video drivers for the new card. Once the system is up and running you might be able to disable the onboard video card in the system bios but it really isn't necessary. Do not remove any of the nvidia drivers because what you remove may be integrated into the operation of the chipset. So best advice from someone thats done what you're doing a number of times.. Plug in the card.. install the drivers.. Have fun..
System Specs: ASRock 970 Extreme3, 8 Gig (4 x 2Gig) G-Skill 1333 DDR3, AMD FX-8150 8 core @ 4.4 Ghz, Thermaltake Water 2.0 Pro liquid cooling, Corsair 1000W PSU, XFX HD7970 Ghz Edition, Windows 7 Ultimate 64