Do your research - the amount of info available on the net about this Intel vs AMD topic is enormous
You are correct though, clock-for-clock coparison between Intel and AMD chips are incorrect and ridiculous, because the architectures are different
The 4400 X2 is an awesome chip, and assuming that you couple it with a quality board, you'll get great results (it is by far superior to the P4 you are currently running)
and a little something to ease the pain of CPU selection (its updated semi-frequently)
http://techreport.com/cpu/