You will not be able to change the multiplier on that CPU, so let's see if these instructions will help you:
ASUS P4C800E Deluxe / MB
P4 Prescott 3.0e / CPU
Corsair Twin X - CMX5123200C2PT / 400mhz / CL2
Zalman CNPS7000A-Cu / Cooler
ATI HD3850 / 512mb / GDDR3 / AGP
How to Overclock using the BIOS and AiOverclocker
First let me tell you that your memory is probably going to hold back anything you do to your CPU because unless you use a better grade of memory your higher settings will mean nothing if your memory lags behind but with this info you should be able to OC a little.
With the P4P800, you should not use the presets:
First go in the BIOS to the advanced settings and "Jumper Free" configuration.
Then lock the AGP/PCI fqcy on 66.66/33.33. Because your RAM is Corsair 3200, you will not be able to overclock at 1:1 ratio (400 MHz) and will have to reduce the ratio to 5:4 (320 MHz) in the "DRAM frequency" setting.
Set the "AI overclock tuner" to "manual". Now you can start to increase the FSB speed under "CPU external frequency".
Do this step by step with steps of 5 MHz and check each time for system stability.
Theoretically, your RAM would be able to support a fsb speed of 250 MHz which brings it back to it's nominal frequency (250*4/5 = 200), but your Prescott CPU will surely not make it without extra cooling and voltage adjustments. You could however expect to be able to reach a 230 MHz fsb speed (cpu at 3.45 MHz) without trouble.
After each new setting, watch your CPU temps with the Asus probe!!!
Note that at that speed your RAM is still underclocked and that depending on the application, this could result in lower total performance. What you win in CPU speed, you loose in RAM speed. Therefore, I would not recommand to overclock your system very high if you don't plan to change your RAM (for example for Corsair PC4000 or higher). You would have to run your current memory voltage up to 2.8V and timings of 3-4-4-8 to OC-doubltful that your memory will hold these timings
Why use this memory the answer is found here:
http://www.pcstats.com/artvnl.cfm?articleID=1907
One last point is about some Asus special features: the "performance mode" and the "memory acceleration mode" (in the chipset settings).
First try to disable them all (MAM disabled, Performance mode on standard), because those could cause your system to refuse to boot. Once you've reached a fsb that's high enough and stable, try to enable the MAM and later to set the performance on turbo. Don't do both operations at the same time.
Just be warned that if your system refuses to boot after too much agressive settings, you will probably need to disconnect the power plug of your system for one or two minutes before it accepts to boot again.
Hope this helps
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