This jumper doesn't change the FSB, it changes the AGP divider ratio. The 66 position will set the AGP divider at 1/1, so if you O/C your Celeron to 100 MHz the AGP clock will be 100 MHz. To O/C your Celeron to 100 MHz, you need to set the jumper to the 100 position to set the AGP divider to 2/3 and the AGP clock will be at 66 MHz. This is referred to as a b21 override capability. This is the way it works on my old Soyo SY-6BB motherboard.
1.Old Antec Case, Asus PC-DL, 2 x 1.6 LV D1 Xeons @ 3 GHz, 2GB Corsair PC3200 @ 200 MHz, Chaintech 6800 128MB AGP
2. Old Crap Beige Case, Gigabyte GA-H55M-S2H, Core i3 530, 4GB CL8 OCZ DDR3-1600, eVGA GTX465
3. Asus Pundit mATX Case, MSI AMD Zacate E350/dual core E350IS-E45 mini-ITX, 4GB CL9 Crucial Ballistix DDR3-1333, LG Blu Ray/HD DVD & DVD Burner