Get Nvidia BIOS editor
here. Use NVmax until you get a stable overclock. When you are happy with your results, use Nvidia BIOS editor to make a custom bios. Then simply flash with custom bios to stay permanently overlocked. (Be sure to backup original bios 1st.)
You can always re-flash bios back to original settings should something go wrong. You can always re-flash bios to a slightly lower clock/memory speed if you find out later that your settings were too aggressive.
The benefit of flashing bios instead of using software overlocking utilities like NVmax is:
1.) no screen flickering during windows startup (a side affect of all software overclockers)
2.) you do not have to re-overlock when reinstalling OS/drivers/other tweaking softwares.
3.) no background startup utilities hogging resources or slowing boot process.
All instructions on web page listed above. It was fairly simple to do. I got my Gainward GeForce3Ti200 permanently overclocked to 230/540. No more fiddling with software tweaks. Truely a set it and forget it solution.