So your going to need good air cooling to OC. A good site that tests coolers in a controlled manor is frostytech.com, for your s939 I would go with the XIGMATEK HDT-S1284EE 120mm Rifle CPU Cooler its $40, its quieter and a top performer. If you have already Arctic Silver 5 thermal paste then you can remove the stuff that comes with the Xigmatech and use the AS5. If you don't already have AS5, then I would suggest to buy a tube of IC Diamond 7 Carat Thermal Compound (1.5g) $7 Petras tech show is very well known and reliable, all extreme PC users use this store. When applying thermal paste its important to not use too much, apply the size of a fully hyrdated (cooked) grain of rice in the center of the CPU. It will spread out evenly from there.
A good place to start to read about OC'ing Techreport Link, and they provide more links in the thread.
When OC'ing its good to use Memtest86+ to test that the memory is stable prior to booting into the OS, if its not stable the OS can potentially become corrupt. After confirming stability and getting into windows, you can use Speedfan to measure the cpu temp. You can use CpuZ (reports settings) to check your HT speed and ram speed. And Prime95 (stress tester) to test that the OC is stable, its good to run speedfan while stress testing just to see how high the cpu temps go.
OC'ing can be addicting to squeeze every last bit out of a system, but its fun too. Just do some reading while your waiting for your new cooler and TIM to arrive and you should be fine. I also have a DFI MB and they are usually excellent for the OC'er, so your off to a good start.