i remember starting this nutshell once or twice in other forums..
AMD. i broke 3 of them due to poor heat solutions P4 i broke one of them due to temper..( they don't bounce well do they?)
amd. depends on fsb and motherboard. 1800's used to run at around 1.5 gig bit strange that they never came out and said this is an AMD 1.5 gig and under the same process i'd emagine AMD 2800 would run at around 2.4 gig, not that this is a true measure of ability, bench test scores seem to come out favourably towards AMD when vetted against P4 on the 533 fsb, but now the 800fsb is around, we should see a large step between the two rivals.. or so they would have us believe.
this will all come down to the user and what he/she will use the system for. for graphics and all things that create heat. eg games dvd burning and ghaphic rendering i would plum for p4 on the 2.66 but for office, internet, tasking and lots of noise i think AMD 2400 or above will make you smile just remember to get an exhaust and some furry dice..