Nothing wrong exactly, it's just that P4s do it a bit better than equivalently priced A64s. That's about the only thing they do better though
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How desperate are you for this system? Windows XP 64 bit edition looks set to finally launch in April, and at that point Intel will probably enable EM64T from the top to the bottom of the P4 range. Video editing is one of the few areas where you could see a speed boost from 64bit. If you do need to buy now, I personally would be quite tempted to put the system together around a S775 Celeron like the 330J (less than £60 from ebuyer). That'll most likely overclock to over 3GHz (possibly well over) and it'll perform well for what you want to do becase
AFAIK cache size doesn't make a huge difference to media encoding work. Then in April you can drop in a 64bit P4 to have a bang up to date system.
Rich :¬)