Here is the guide I started off with.. http://pc.ign.com/articles/747/747606p1.html
I'm running a similar system as you. I just (yesterday) installed a Cooler Master N520 CPU cooler & a Creative SB X-Fi PCI-E card, I lapped both the E6600 & N520 up to 2000 grit. I used Arctic Silver 5 & my temps (at stock 2.4GHz) went from 33-35c idol w/the stock cooler to 26-29C w/the N520.
Remember.. Take baby steps when overclocking! Good Luck, Phil B.
Case: Cooler Master HAF 922
CPU: Intel Core 2 Duo E6600 2.4 MHz
Graphics Card: EVGA 8800GTS 640 OVERCLOCKED: GPU MHz: 620 RAM MHz: 1000
Hard Drive(s): System: Western Digital VelociRaptor 300GB SATA 6 Gb/s 32MB Cache. Storage: Seagate 250GB Barracuda 7200.10 SATA II 16MB Cache
RAM: OCZ 2x512 & 2x1GB Gold GX XTC PC2-6400.
Power Supply: CORSAIR TX650W
Motherboard: EVGA 680i SLI A2 122-CK-NF68