Oh, it’s not brain surgery.
Chances are the sweet spot for your PIII 550 is at 733 MHz. Your front side bus is currently 100 and your multiplier is 5.5. Knocking that FSB up to 133 should get you to 733. That’s a 33% boost right off the top. There are several things you need to do to get there.
First, you have to back everything up. One of the most common errors you will experience when overclocking too far is a disk-write error which oftentimes requires you to wipe the hard drive and reinstall everything. Hey, man, you’re making a new computer here anyway, right?
Second, you must adjust your core voltage upward. If you’re lucky enough to have an Abit or a Soyo motherboard, chances are you can do this within the BIOS settings. Otherwise, you’re going to have to determine what kind of motherboard you have, find a diagram for it, and find which jumpers need to be moved where. Hopefully, you have the manual for it. I think your default voltage is 1.50. You’ll probably want to kick it up to 1.60 for starters, and graduate it to 1.65 if you find your system to be unstable. Do not go above 1.8. That is well within the law of diminishing returns, and can permanently damage things.
Third, you must also adjust the front side bus up to 133. Even though your BIOS offers setting changes, you must make certain that you are adjusting the FSB and not the clock multiplier. Your multiplier is locked at 5.5 and cannot be changed. If 133 doesn’t work (probably because of your PCI devices), you can try using other, lower settings, if you have them.
Fourth, you must carefully monitor your PCI components. These are things like network cards, internal modems, a few graphics cards like some Voodoos, and sound cards. The PCI bus works by dividing the front side bus and defaults at 33 MHz. Therefore your PCI divider is currently set at 3. If you’re very lucky, you may be able to change the PCI divider to 4. Otherwise, you’re going to have to pray that everything holds together at 44 MHz. If it doesn’t, start by removing your network card and replace it with a good one or just toss it if you don’t use it. Cheap NICs are notorious for flaking out at high PCI bus speeds and bringing the whole system down, but the Intel NICs, which run around fifty bucks, are pretty stable.
Fourth, don’t take my word for it. Instead, go read up on how to overclock at places like the Ars Technica OpenForum, the cold, [H]ard, OCP, and of course, www.overclockers.com . The PIII 550E was a quite popular target for OCing for many moons, so you should find all sorts of good information in those places.
I have a chumpy little Celeron 533A which purrs along at 892 MHz and has for the past two years without any major problems (except that I can almost get it to 936, and every time I try I smoke all my data and have to reinstall Windows). It’s fun, you’ll learn a lot, and you’ll save a crapload of money on your next computer because there will be no way in hell that you will let anyone else build it but you.