This thread is a good place to start:
http://forums.anandtech.com/showthread.php?t=47089
I strongly recommend testing all changes with utilities burned on a CD or DVD, with all HDD's disabled. Google "UBCD", download the latest ISO, and burn to a disk. AFAIK, it still has no cpu utilities capable of testing anything beyond core 0, but it may have changed since I last checked.
Before you boot from your O/S for the first time after overclocking, be prepared for trouble... back up anything important, and if possible, clone your HDD to another. It's no fun if you corrupt the boot sector and have to connect the drive to another PC to back up everything.