"The CPUs at the heart of these two consoles are very different in architecture approach, despite sharing some common parts. The Xbox 360’s CPU, codenamed Xenon, takes a general purpose approach to microprocessor design and implements three general purpose PowerPC cores, meaning they can execute any type of code and will do it relatively well.The article can be found here
The PlayStation 3’s CPU, the Cell processor, pairs a general purpose PowerPC Processing Element (PPE, very similar to one core from Xenon) with 7 working Synergistic Processing Elements (SPEs) that are more specialized hardware designed to execute certain types of code."
PS3 and Xbox 360 - technical comparision

Thousands of articles have already been posted about Microsoft's upcoming Xbox 360 and Sony's PlayStation 3 but AnandTech decided to carefully investigated the technical features of each consoles and posted its thoughts. Here's a short snip: