Let me walk you through it in a little more detail. Your turbo switch on the case has a connector on the end of the cable. It is probably a 3-pin connector. You only need to use two of those pins. Pick any two adjacent pins. The switch connects and disconnects those pins at the end of the switch when you push the button. The button's pushed in position will either be with the pins connected or disconnected, depending on which two adjacent pins you select.
On the M919 motherboard, when JP3A has a jumper on it, the FSB is at 33 MHz. When the jumper is removed, the FSB goes to 40 MHz. The turbo switch can take the place of the jumper. Be sure to leave JP3B and JP3C jumpered. Determine if the out or in button position is with the pins are connected or open. What idspispopd was suggesting is to boot the computer with JP3A switched closed (BIOS should detect an AMD 5x86-133 on startup). Then once you past the POST screen (and presumably the computer is idle), hit the switch and the FSB will run at 40 MHz. You should now have a PCI bus at 40 MHz because you have now passed the CMOS's startup routine which was trying to automatically adjust your PCI bus.
idspispopd, on this motherboard, the PCI bus does not get divided in half, it is multiplied by 2 and divided by 3.
Plan your life wisely, you'll be dead before you know it.