Knowing the motherboard model number would help a lot.
Start by making sure that ANY reference to AGP is disabled in BIOS settings.
Also, make sure that the first video device is set to PCI.
The VGA driver for the chip-set may do 1 or 2 things that W9X is ignoring.
First, the chip-set VGA driver usually installs the display driver for on-board video.
The chip-set driver may also install the AGP mini-port driver.
I suspect the W9X is ignoring both the on-board video driver, and the AGP port driver.
W2K is attempting to use the "new" hardware that does not exist.
I recommend installing ONLY the INF and IDE drivers for the chip-set.
Another possibility, is that Gigabyte is using a 'customized' driver that bypasses themissing hardware.
If there is anything out of the ordinary with the motherboard design, I usually stick with the motherboard manufactures drivers.
Chas