In my opinion, this is what you should do:
1. Make sure that you have a decent HSF and that your CPU has been properly unlocked.
2. Turn off jumperfree mode, since from my experience it leads to some weird issues when trying to OC.
3. Up the voltage to 1.85v, see if it POSTs. (make sure you keep track of the temps. watch out for anything above 50-55C)
4. Up the multiplier in 0.5 increments. (ie next step should be 6.5X100=650MHz). Do this until you can't boot anymore, then set to the last one you could boot at.
5. Up the FSB if you want.
If you find that some multipliers are missing, or that you can get farther with FSB OCing than multiplier OCing, then chances are that the bridges are not connected well enough.