basically... if you read this...
http://www.amd.com/us-en/Processors/..._177_3472_1353^3841^9078^3759,00.html
basically... intel p4 does 6 instructions per cycle vs. 9 instructions per cycle in an athlon... this is where the performance rating is derived from... so an athlon xp2800+ can perform at 2800mhz compared to an intel but is only running at 2.09ghz... a amdxp3200+ running at 2.2ghz can easily compete with a p4 3.2ghz... but it also depends on the application
hope that helps