If you know what your FSB speed, it is easy to figure out. If you don't have.....example follows
If you are running yrou system at 133Mhz FSB, you are normally using a 1/4 divider......1/4 or 133 is 33Mhz. This is your PCI bus speed. After you figure that out, you AGP speed is always double your PCI speed.
So the only thing you ever need to know is the FSB and your divider and you can figure out the rest. BTW, most people don't get there PCI bus running stably at more then 41Mhz