Ati radeon 9600 video card not working

I have a pm4dpt motherboard and I am trying to get this ati radeon 9600 to work with it but I am not having any success with it
The on board vga is working but when I try to use the agp card I get a message on the screen something about "cannot display this video mode"
In bios I have the option of selecting onboard, pci or agp this is for "Initial display" which I am not sure what it means.
Does that mean that initially starts in one mode and then switches to another mode ?
If so what determines when to make the switch ?
Somehow I don't see that working unless the agp card has a bypass for onboard vga
Another question is do the drivers have to be installed in order for this card to be able to display anything on the screen like the bios for example ?