Disable onboard video card

I have WINXP (SP1) and my chip set has an onboard video card. I have a RADEON 9000 64 MB DDR video card. I have the latest driver as of (10JUL04) and Direct X 9.1. My video works fine during desktop and some low end games, but when I goto a highend game, the monitor losses its signal and I have to reboot. Someone told me it could be the sound too. I was also told the registry looks for the onboard card and the two clash and there is no fix except for a new board with out an onborad. Is this a useless attemp at wasting my time playing games? I appreciate anyones time to try and help me. Board in the desert, Scott.