For 24/7 use, keep the temps around 60C +/- a few degrees. The stock cooler won't get you far, as you may be close to that already.
You have the take the multiplier higher. You have a 200Mhz FSB (front side bus) and that is multiplied by the multiplier. 200Mhz x 15.5 multiplier gives you 3.1Ghz. You have to set that multiplier higher. So, to get 3.2Ghz, set the multiplier to 16 instead of 15.5. If you get a crash, add voltage. Adding too much voltage can kill the CPU, and adding voltage adds heat. Test the CPU with Prime95 for 6 hours to ensure stability while monitoring temps and voltages with Hardware monitor.
You voltage should not be set past 1.5v I think. I would stay under 1.45v for long life.
So, take the multiplier up, add small amounts of voltage if you get a crash (.01v), and go from there. Remember, too much voltage can kill the CPU, and for 24/7 use don't go past 60C +/- a few degrees.