Start by downloading and installing Prime95 25.6, and the newest version of CoreTemp. Increase your FSB in the BIOS, boot into windows, and run prime95 "torture test", "Small FFTs" for 10 minutes until you get an error. If get an error, then increase the vcore. If you don't get an error, increase the FSB again. Keep doing this until CoreTemp tells you that your chip is running too hot (70C or higher), or your vcore setting exceeds a safe value. For 65nm chips, I believe that value is something around 1.5v vcore. Oh yes, also download the newest CPU-Z, and run that. It will show you your vcore under load (running Prime95). The vcore under load will read a lower value than what you entered in the BIOS. That is because of vdrop (difference between BIOS setting and measured idle voltage) and vdroop (difference between measured idle voltage, and measured load voltage). Some amounts of vdroop are normal.
With my E2140s, I got to 3.2Ghz using BIOS vcore of 1.425v, which is around 1.36v under load as measured by CPU-Z. My temps, with a CoolerMaster HyperTX2 cooler, load at 80C. I hit my temp limits, and my overclocking goal, so I stopped there. Btw, the E2140 default Mhz is 1.6Ghz. So I achieved a 100% overclock. Not too bad for a cheap chip.
Also, you might want to flash to BIOS 18 (before you start overclocking). At least with a 45nm E5200 chip, the newer BIOS greatly reduced the vdroop that I saw.