OH OH OH, I THINK I KNOW WHAT IT IS NOW!!!!!! i didnt read your first post very well but you said its a AGP 2x card. that wont work in a motherboard that supports 4x! heres how it goes:
AGP 4x and 8x = 1.5v (meaning they use 1.5 volts to function)
AGP 1x and 2x = 3.3v (or something around there... maybe 3.2)
so anyway, the old AGP 1x and 2x style cards run on different ammounts of voltages and depending on your motherboard, it will only run AGP 1x and 2x or AGP 4x and 8x. thats why your radeon works, its an 8x (well, it might be a 4x, but it doesnt really matter). man, i really need to look at posts more closely!