Overclocking is not that hard, specially when dealing with Core 2 Duo's...
Unfortunately I am not familiar with the Nvidia 680i boards.
But this is the basic idea behind overclocking:
Your E6600 has a multiplier of 9 and your default FSB is 266 mhz.
The ram speed required for your system is DDR2 533mhz (2 X FSB)
To overclock your system (basic overclocking) you will simply need to raise the FSB and that will give you you're target speed.
Your RAM runs @ 800mhz, if you divide that by 2, then your RAM will be able to handle at least a 400 FSB (2 X FSB = 800mhz)
And a 400 FSB X 9 multiplier and memory running @ DDR2 800mhz = 3.6ghz.
350 FSB X 9 DDR2 700mhz = 3150
and so on...
Now, you need to set your RAM timings in the BIOS, manually, as well as the default Voltage recommended for your RAM (check the specifications)
Now, start small.
Try 300 FSB X 9 which should be done easily.
You will then encounter a problem when you go too high and that's when you'll need to change your cpu's default voltage. (1.288V
If you have a good chip, it will do 3.6ghz with 1.5V or less
The more voltage the higher the temperature it will be. BTW, your temperatures are a little high for a CPU running @ default speeds.
Oh, and your CPU cooler is not that good. Think of upgrading to a Tuniq Tower 120, Scythe Infinity or Thermalright Utra 120.
If you want to learn more, go to
www.xtremesystems.org/forums and read through the forums. Lots of help there...