The His Excalibur Radeon 9800 Pro has a bus interface of AGP 8X/4X. So in theory the card should work in your 4x AGP slot. The down side is that you will be only using half of the pipelines on the video card.
What is the wattage of your power supply?
What is the voltage setting in your Bios for the AGP slot?
What version is the AGP slot - 1.0,2.0 or 3.0?
I know there have been issues with Intel chip-sets regarding this.