Hi Basserho
From what you say it appears that the speed is this as soon as you switch your machine on. Assuming this happens when the machine hasn't been on for a little while ie cold, it suggests it isn't an overheating problem.
Right, it looks like your FSB (Front Side Bus) speed has been changed to 100Hz, rather than the 133Hz it should be running at.
The AMD XP1500 chip is as you say a 1.33GHz, this is derrived from a FSB of 133 and an internal multiplier of 10x. Therefore simple mathematics 133x10 gives the chip speed.
Had you had a system crash or something recently? this could have caused the problem. Or have you put in some new memory (the memory being 200Hz DDR)?
Now to restore the problem you will have to go into the BIOS, you get this as it is just booting up, you will have to press the 'Del' key (or whatever your system requires) and you will enter the BIOS.
There should be a setting for CPU speed or FSB speed, this should be set to 133Hz. It will probably be in the page named 'Advanced' in the BIOS.
I'm not sure where exactly it will be in your BIOS, as I don't know what BIOS you have.
I hope this helps, and will get you XP motoring along again at full speed
Nice to see another local northern lad too