Surely I can overclock this Prescott more!

I had my CPU overclocked to 3.359 GHz, and it's stable. If I try to go any higher, Prime95 gives me errors. At the moment I have my CPU External Frequency set to 224/37, my Vcore set to 1.3500 (I tried raising it but then I can't boot into Windows). My Memory Frequency is set to 448. If I set it to 372, I can't boot into Windows, so it seems I'm stuck with a ratio of 1:1 at the moment, as opposed to the recommended 5:4 for this Prescott. DDR Voltage Adjustment is set to Auto. All memory timings are also at auto. My temperature is around 43 idle with stock cooler.
Any suggestions?

You are going to have to buy a real motherboard. The 'S' in P4S800 stands for SiS, as in the board is based on a SiS chipset. While not horrible chipsets, using one instead of an Intel chipset will almost always limit your OC. You need a P4C800 (Canterwood, i875) Asus or other quality i875 mb to maximize your OC.

Also, ram needs to be evaluated. Some late model Micron 3200 is very good, most older stuff is terrible. Whichever flavor you have you need to make sure you aren't trying to run it too fast or use too tight of timings and limiting the OC that way.

Try and get hold of a IC7 Max 3. You could try relaxing the ram timings abit. Set the vdimm to up a notch and stick to 5:4. For vcore, each mobo has different settings, on the max 3, setting the vcore of 1.5325v is actually 1.5v straight when idle. On your rig, I am sure you should be able to reach 3.5Ghz or fsb:220 with no problems. Also, read a few post on other bios settings. Disable the video and bios caching, setting the agp to higher voltage is known to help in some mobos. If you really want to OC the cpu as high as possible then your gonna need some new ram and a new cooler. I have never used the standard intel cooler. I heard people getting good results with the zalman HSF. What version of the pressy is it? co or do? CO dont tend to C0 well. Also, dont forget to enable the full ls cache in xp.

Good luck.

Thanks for the help.
By the way, I'm already at FSB 220 (3.359 GHz). I want to go higher.
Also, it's a C0.
I'll try a few of your suggestions.

I just re-read your post and see you haven't increased memory voltage. Definitely try that. If you can select 5:4 mode try that. But do bear in mind all the stellar P4 OCs you see are done on Intel chipsets--so if the exact magnitude of the OC is priority one another mb isn't too steep a price to pay.

In the OC game, the man who trys the most parts wins. Chaulk it up to experience, order up a P4C800-E or IC7-Max3 and ebay the P4S800. Be prepared to do the same with the ram if it doesn't walk just right. Nobody said this OC stuff was cheap.. heh.

Obviously, your system works fine as-is and is pretty fast. Further gains will be somewhat costly and of minor importance to its exact function. It's more a personal satisfaction thing than a rational pursuit. But since you asked, I have outlined what I would do if it were mine and I cared about the OC. Good Luck.

Thanks
Actually, I have tried all sorts of combinations to get the 5:4 ratio, including increasing the memory voltage. Nothing allows me to boot into Windows. I've even tried another DIMM slot on the motherboard.
Actually I think I'll leave it at that for now though. Next time I buy a motherboard, I'll make sure it's a little more overclocker friendly, but I just bought this motherboard/CPU combo off eBay a month ago. Would be a waste of money to sell it and buy a new one just yet. I'll wait 'til maybe next week.