Starting from the top
The AMD 64's use different archecture, so are more efficient, and that number is the average equivilant of 'the main competitor' would need to have to compare to it. The AMD's actual processor speed is not that high. The FX57 (The top gaming proccessor) is 2.8ghz, but due to having shorter pipelines, it can do more calculations per cycle , it can do alot more with that 2.8ghz.
The 2ghz is the hypertransport speed, with a bus speed of 200mhz. AMD doesn't use a FSB as it is not efficient, so instead have a onboard memory controller, and a link to the memory at 2000mhz.
They are both nearing that brick wall, where they can't go any higher (on the 90nm archetecture.) So what they are doing is having more cores on the chip, and let the programmers make use of those cores, to work on the same program together.
With AMD you have to ignore that pure clock speed, as it isn't a representation of what it is capable of. Even comparing a 2ghz socket 939 to a 3ghz socket 754 isn't a accurate representation. So you have to look at benchtests.
When the memory is running slower than the bus speed, that is when the bottlenecks happen (under 200mhz.) AMD will move onto DDR2 at 667mhz for their next socket, the M2. Also AMD make full use of dual channel ram, with PC3200 ram, would nomally transfer data at 3200mb/s, with dual channel it runs at 6400mb/s. Intel systems don't get bandwidth as high as that with dual channel.
Btw. there is a search button.