What that means is your Overclock is not stable. You cannot simply just go into the BIOS and change the clock speed to whatever you want and have it work properly.
You'll want to make sure that you turn of anything to do with Spread Spectrum in the BIOS as this is only to reduce the amount of EFI given off by the cpu. It does it by constantly varying your clock speeds, which can make a pc unstable when overclocked.
EDIT: Just looked in your Manual and under the Extreme Tweaker tab in the BIOS, you'll want to disable CPU and PCI-E Spread Spectrum. They are all the way to the bottom. You'll also want to goto the Advanced tab and choose CPU Configuration. Disable Intel SpeedStep, otherwise your CPU will try to downclock itself when it's not being used.
As for voltages the best advice that I've read is just leave it set to auto as most boards now can adjust this properly. You might not get as high of an OC that way but if you don't know what all of them do, it's best to not start upping the voltages randomly.
The next point to consider is your divider. It's usually best to keep the ram below it's rated speed while trying to OC the processor. This makes it easier to figure out how high you can get the processor. Then you can go back and adjust it for ram.
What you're going to want to do is slightly up the fsb maybe 25mhz at a time and make sure it posts. Every 100mhz boot into windows and run something like Prime95 and make sure that it can pass for at least 10 minutes. Once you get closer to where it doesn't like to be stable back it off a little and bench it again. Then write that number down.
Put the FSB back to stock then start raising the multiplier .5x at a time until you figure out how high that will go. This gives you the maximum clock speed to run the processor at. From there you can find a happy medium so you can run your ram at it's rated speed, and still have a good OC.
When you goto bench with Prime95 always make sure to monitor your temps with a program like realtemp or HWmonitor. I use both as they vary a little bit. For your processor I think your maximum temp should be 65C. http://download.intel.com/design/pro...hts/318726.pdf
If you go over that what happens is the CPU will send the PROCHOT signal and start throttling itself so it won't overheat. Realtemp will show you if any of the processors have flagged. If they have then it means you need to back off your OC as it's generating too much heat. This is definitely one way that a program might be slowing down. The other is if the OC is not stable it will be using bad data which can cause crashes and slow performance.
I would suggest skimming this article: http://www.anandtech.com/cpuchipsets...spx?i=3184&p=1
It also wouldn't hurt to google a few other OC articles if something isn't making sense. You can post questions here and someone might also know the answer. Good luck and happy OC'ing.
EDIT: From our tutorial thread. This link has some decent information in it as well. http://www.ocforums.com/showthread.php?t=515316