is your computer made by like a major computer manufacturer. If it is then it most likely won't have a option in the bios cuz the manufacturer wants you to have to go out and buy a new computer in order for you to upgrade you system.
Well it certainly SHOULD be that way, but this was a really weird setup.. totally jumperless, two PCI slots, and NO way to disable the onboard video. I literally searched that thing for an hour looking for a jumper or something, but no such luck. According to a post I found on a forum, it was supposed to disable the onboard automatically when you put a PCI video card in the top slot, but I tried that with 3 different cards and it didn't work.