I have to agree with the other guys. Then again, if you don't want to build your own, I suggest you buy either a computer with P4 using RDRAM or an AthlonXP.
The reason I am saying this is because I think I remember reading an article by THG that P4's get the best performance out of RDRAM and even DDR slows it down instead of helping.
It has also been proven that the AthlonXP using DDR is faster than the P4 (for now). At any rate, I would wait until after the first quarter of the year is over. Some price drops should be coming.
