Never heard of AGP express
I have been reading the PDF manual for your mobo and the specifications for your GFX card.
1.8.5 AGP slot
When you buy an AGP card, make sure that you ask for specification. Note the notches on the card golden fingers they fit the AGP slot on your mother board. Install only 1.5V or 0.8V AGP cards on this motherboard!
motherboard does not support 3.3V AGP cards.
Graphics Adapter Priority [AGP/Int-VGA]
Allows you to select the graphics adapter to use as primary boot device.
Configuration options: [Internal VGA] [AGP/Int-VGA][AGP/PCI] [PCI/AGP] [PCI/Int-VGA]
Asus PDF Manual doesnt show advanced bios options so I cant see the other settings.
ATI Radeon 9200 series :
System Requirements
compatible with AGP 2X (3.3V), 4X (1.5V), 8X (0.8v) or Universal AGP 3.0 bus configuration (2X/4X/8X) or PCI bus.
The AGP card should run at 8x if its auto detecting it and dropping the voltage to 0.8v, if its sticking at 4v for some reason then it may only be allowing it to run at 4x on boot up and maybe it doesnt support the texture acceleration unless its at 8 x
Have you got the Graphic adapter priority set to AGP/PCI ?
Other than that I cant see anything else that you can alter unless theres something in the advanced settings that I cant see in the PDF manual.