This should be your first stop.
HOWTO: Overclock C2Q (Quads) and C2D (Duals) - Guide v1.6.1http://www.tomshardware.com/forum/240001-29-howto-overclock-quads-duals-guide
Next stop should be a guide for your particular motherboard. Google is your friend.
Go through the guides. Then go into the BIOS and change the System Memory Multiplier (or whatever your BIOS calls it) from AUTO to 2.00, 2.00B, or 2.00D - whichever you need to set the Memory Frequency to twice the FSB. Then when you increase the FSB, the memory clock will rise in step with it. If you are at stock speed, your FSB should be 200 MHz and your memory clock should be at 400 MHz.
For a serious overclock, you will need better than stock cooling. This is pretty popular:
COOLER MASTER Hyper 212 Plushttp://www.newegg.com/Product/Product.aspx?Item=N82E16835103065
Suggestions for applying thermal compound:http://benchmarkreviews.com/index.php?option=com_content&task=view&id=170&Itemid=1&limit=1&limitstart=5