Multipliers on all Intel CPUs (modern ones anyway) are locked, so changing it won't have any effect.
To overclock an intel, you have to adjust the FSB (front side bus) speed. Your CPU is at 66 by default. If your board has bus speed options, you'll want to change that. If you're really lucky, you can change in in increments of 1 (67, 68, etc). If not, maybe you can change it to 75, 83, and then to 100 or more.
Check in your BIOS and try to find the FSB adjustments if they're there. Try raising it to the next one available (unless it's 100). Then save and exit. If you can do that, you're overclocked!
Before making any changes you should find the Clear CMOS jumper on your motherboard. If something screws up and the computer won't boot after changing the bus speed, unplug the power cord and clear your CMOS. That will restore everything in the BIOS to defaults and then you'll be able to reboot.
There are some good reads in our Beginner's Guides
here that go over the important stuff like that. They are worth the time reading because they'll save you many headaches.