Answer
This question was answered on February 15, 2006.
Much of the information contained herein may have changed since posting.
The first thing you should do is pull out your maunal for your motherboard. Some motherboards have jumpers or specific settings in the BIOS to disable onboard components. Other motherboards have a setting that lets you switch between "Onboard AGp" and an add-on card. If cant find your manual or you didnt build your computer yourself I would find out what kind of motherboard you have and then go to that manufacturers web-site. Most sites will have Manuals often in Adobe PDF format free for download.