first off dont put in the card yet. boot to ur desktop then go to control panel. go to system and hardware then device manager. go to display adapter and right click on whatever is there and click disable. once uve done dis...shut down. open ur case then install the new gfx card. then follow instructions from card manufacturer.
also just out of curiosity, y did u go with an ati x700 when a nvidia 6600gt performs better and is cheaper.
I just upgraded to an ati x700 pro and can't figure out the bios menu (i can get to the bios - i just don't understand it). There's no specific mention of on-board video that i can see (just a bunch of bios acronyms). Obviously, i'm no computer expert and would appreciate if someone could tell me EXACTLY how to disable the on-board video on this machine. It's a stock machine from Circuit City, so all stock system information applies. Thanks, in advance!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic