Go through the guides. Then take your core voltage off Auto and set your memory voltage to factory recommended values. Change the System Memory Multiplier from AUTO Then when you increase the FSB, the memory clock will rise in in proportion with it. At an FSB of 266 MHz, your memory clock should be at 533 MHz.
Keep your core voltage under 1.45 volts and your load temps under 70 C.
I have that exact same cpu on another computer and it can handle most things I throw at it (can not do what my i7 can) You also need to ask yourself what do I use it for? For what I use it for does it lag or does it do okay. You can over clock but unless you render videos or other cpu intense stuff, then do not need to. Also if you want to over clock. Make sure to get an after market cpu cooler. If you do not already have thermal paste I would recommend Arctic Silver 5. Make sure you know exactly what you are doing when/if you attempt this.