an AMD 3000+ is equivalent to a 3.0 Intell.
though the AMD is much cheaper for its price per performance cost, making it a better deal.. it will perform worse though on such tasks as Variouse win applications, and Vidoe prosseccing, simply cause it has a lower clock speed... but graphic wise it performse better.
So depending on your use for hte computer, choose witch better suits you. also, the intells are better at multitasking then tha AMD XPs because Intell has hyperthreading.
I dont know much about the AMD 64's or there pricess, but thy have a much higher Bus speed then the Xp's, because of there Hypertransport technology. but you can always check into those pricess, i dont have a clue what thy r, but i think thy have been dropping fast in price recently.