the 2ghz p4 hands down, 1 2ghz cpu will make less heat then 2 1 ghz cpus. also , 2 cpus are for multi threading, so if there was 2 threads, and it takes a 1 ghz cpu 5seconds to do it, it would take 5 seconds for it to do 2 threads becasuse it has 2 cpus. with 1 it would be alot slower, however, the p4 is twice as fast so, it does 1 thread in 2.5 seconds right after another of 2.5 seconds, so each can do the same at most. but what if there is only 1 thread, it will take the dual 5 seconds to do it becuase on a single thread of data, a dual uses 50% of each cpu. but if it were the same single thread in a p4, would be in 2.5 seconds. So getthe p4, it is faster in single threaded things, and both are even in multi threaded. hope this is not to complicated for ya.