Pretty sure that the processor you have does not have an unlocked multi I could be wrong though.
So wait for someone else to chim in.
Now I could recit the entire advice of overclocking word for word.
But I won't, because I lazy!
So I will just link you to ths VERY good overclocking Guide.
Core2Duo Overclocking Guide v1.1
In the end its not that hard. The basics, the extreme basics Are:
Up CPU frequency > test for stability > if stable, then more CPU frequency increases, if not stable adjust/modify Any combination or Vcore, RAM Voltage, FSB voltage, MCH voltage and memory timmings.
Continue in a loop.