Please search, this has been covered numerous times.
AMD clock cylcles can process more instructions than Intel clock cycles and gradual grow more and more effective with each generation. Therefore an AMD processor can use a smaller frequency than Intel yet still process the same amount at the same speed.
To put it simply this is because AMD uses shorter pipelines, which provides performance in "horsepower" applications, or more specifically, games. AMD can send more data out faster with each clock cycle, but not as much.
Intel on the other hand uses long pipelines. They excel in rendering, encoding, and other extensive CPU intensive applications. Intel takes a lot of data at once and processes it over an extended period of time, or takes more clock cycles.
The AMD naming scheme was introduced to give users a comparison between their chips, and those of Intel. In theory an Athlon 3200+ is the competitor of the 3.2GHz Intel Pentium 4, however due to their differences in architechture as mentioned above each excel in a variety of fields.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w