the theroy of overclocking is very easy. SImply increase your frontside bus higher than the deafult 133 your clock speed willl then go up by X amount ie 150x12.5=1875mhz.
Now thats the very basics out of the way.
When overclocking your FSB you will also be increasing the speed of the PCI/AGP bus these will run well out of spec at a 150 overclock theis may casue cards to die or data to get corrupted. then comes the more advanced method of overlcokcing. with and Athlon XP you can unlock the mulitplier by closing the level1 bridges(there are guides all over on how to do this) this will allow you (motherboard permitting) to change you mulitpler and thus increase your front side bus even higher.eg 10X180=1800 similar overclock as before but with greater bandwidth due to the incresed FSB. also most new motherboards will have a 1/5 divider so once above 166 you PCI/AGP speeds are running back closer to spec speeds.
Now all the degree of sucess you have with the above will be totally dependent on all your hardware. The processor maybe crap and not overclock very well, your motherboard may not have any FSB settings or voltage settings.
As is the cae with most overclocked systems the motherboards are bought with this puprose in mind so they will have all the different voltage settings and so on. Also if you do have a decent motherboard you can oveclock further by applying more volatge to the CPU however this will casue alot more heat so make sure your cooling is up to it. Generic or OEM HSF will not be up to the job. also i wouldnt recoomend goign up 1.95 vcore on air cooling. and on on great air colling at that.
The memory you use will also be a factor cheap memory will restrict your overclock probably before your cpu does.
The 2000xp can be pushed quite far i have a 2000xp running at 10x176 which is about 60mhz of being a 2400+. so the benefits are worth the effort.
How exaclty you do all the cannot be explained without a greater idea about your system we will need to know you Motherboard , cooling you memory specs is it sdram or ddr? if its ddr what speed is it? without those im afraid a general overview is all the hlep we can offer.