Honestly, if you are unsure on how to overclock your machine properly then the only safe suggestion I can give you is "DONT DO IT"!!
Before you even attempt such a thing get on the net and do as much research as possible on the subjuct! Read Read Read!
If you overclock to much and dont know what you are doing then you can stuff you whole system! And I certainly dont want to give you advice on it as if it all goes horribly wrong I dont want to feel responsible!
