Ok, i will try to give you the most un biased information i can give, there will be some bias, as every bit of any infromation has at least a tiny bit to some deggree:
AMD systems all together are generally cheaper.
AMD athlon xp cpus are cheaper then the intel penitum 4 based cpus to a certain point, an athlon xp 2000+ is about the same as a 2ghz p4, but an athlon xp 2600 is slower then a p4 2.4C, hyper threading and 800 mhz fsb really helps the intel cpu jump leaps and bounds faster then it was before.
Intel's top end cpu is a good deal faster then amd's top end cpu.
i think i have a pretty good explanation here: 2.2 ghz and lower(2200 and lower for amd) amd's pr rating is very accurate, the 2400 would be accurate, but the 2.4c that came out is faster then the 2.4. the barton pr rating is a little messed up imho, it would be right all the way if intel kept the willamett core, but northwood has changed that, and right now, if i had all the money i needed, my desk would have the ultimate pentium 4 setup, however, the ultimate athlon xp setup would perform pretty close, anywhere from 5 - 20% slower is my guess, But correct me if im mistaken, the athlon xp setup would be cheaper, but in return it is slower. The athlon xp also runs hotter then the p4. clock for clock however, the athlon xp is faster then a p4, a 2.2ghz athlon xp would mop the floor ith a p4 at 2.2ghz. But, 2.2ghz is athlon xp's most top end setup, pentium 4 has 3.2ghz, and that makes the difference to come up with the following solution.
You Get What You Pay For.