Lyon, to be safe when overclocking:

Change only your CPU Clock up incementally. With i7 920, your Multiplier will be 21x (with Turbo enabled) and your FSB Frequency (CPU Clock) will be 133.

Change your CPU Clock to 160 to start out with. This will get you to ~3.3 GHz. Save and Exit, allowing your PC to get past POST. If this is successful, go to www.memtest.org and download an ISO for their latest memtest86 program. You need to burn it as a bootable CD.

Restart your comp, changing BIOS to boot from the CD drive to run this Memtest. If your PC passes, you are OK to proceed with either being happy with your current Overclocking, or you can try for higher speeds.

If you want higher speeds, I recommend reviewing this post:
http://www.clunk.org.uk/forums/overc...beginners.html

Start out only changing CPU Clock. Don't change voltage levels if you don't have to. Increasing Voltage won't necessarily fry your CPU, but it will cause it to generate more heat, which might be a bad thing if your cooling system is inadequate.

As an example, I have a i7 950, and overclocked it to 3.6 GHz just by changing the CPU Clock to 160Hz (up from 133). This gives a pretty good improvement when 5-boxing Rift. I stuttered quite a bit at lower frequencies.
(You have a 920, so simply moving your CPU Clock to 160 will give you less than 3.6GHz, but an improvement none-the-less).

Also, If you PC doesn't POST, shut it down, wait a couple seconds and reboot it. Your BIOS should prompt you to reconfigure settings as the previous POST failed. As long as you aren't messing with Voltages, there is a very small chance any harm will come to your PC.