Okay, let me give you the desktop scene in a nutshell....
Intel has lost out to AMD in the performance game. The fastest AMD processors are, for the most part, faster than the fastest Intel processors. What's more, AMD chips are still a lot cheaper than Intel's. So it really doesn't make much sense to buy Intel, anymore, for a desktop system.
The MHz race is over. Neither Intel nor AMD identify their processors by clock speed, anymore. Intel uses a crazy three-digit naming scheme where the first digit represents the type, and the second and third digits (as one number) represent performance. So, for example, the Pentium 4 540 is faster than the Pentium 4 530. The Pentium 4 630 and 640 have a similar relationship, and are considered faster than the 530 and 540, respectively. These are called 5xx and 6xx processors, by the way.
AMD uses a much better naming scheme, based on the old MHz race. The top AMD mainstream CPU is the Athlon 64 4000+, and the bottom model is the Athlon 64 2800+. In between, we have the 3000+, 3200+, 3400+, 3500+, 3700+ and 3800+. Some major-brand vendors have oddities like the Athlon 64 3300+. But, in all cases, the higher the model number, the faster the CPU.
Below the Athlon 64, we have the Athlon XP. Note that the top model Athlon XP 3200+ is slower than the bottom model Athlon 64 2800+, despite having a higher rating. In that sense, the model numbers are not comparable, but within each group, they're pretty accurate. The Athlon XP model numbering goes all the way down to 1500+, and, as mentioned just now, up through the 3200+.
Finally, we have the AMD Sempron. The Sempron model numbering is very confusing, and I suggest looking at benchmarks to find out how they compare to the Athlon 64 and Athlon XP.
....is that what you wanted?