100/133 Jumper

What does the 100/133 jumper on the motherboard do?

I am running a Duron (Spitfire) 900Mhz @ 1000Mhz (133x7.5).
When I leave the jumper at 100 and change the FSB from the BIOS to 133 it works. But when I change the jumper to 133 it just stops. It does not even POST and I have to change the jumper back to 100 and press 'INSERT' just to get to the bios.

Please help

the 100/133 jumper is the FSB jumper. it set the default FSB of your cpu, and your Duron is running on 100Mhz i think...and Althon is running at 133.