The AGP slot and slot 1 aren't the only interfaces that share an IRQ. Check your MB user manual for more. Like that instruction said, disable in the BIOS any interfaces you don't use (serial, parallel, etc.). You can also try to catch the list of IRQ usage on the POST, but you need to read fast for that. You may never be able to avoid sharing all together, but you should look for the most forgiving set-up.