I remain to be convinced in the effectiveness and efficiency of dual processors. They only seem worthwhile in mega-hyper companies with billions of dollars to spend, and who absolutely need to spend twice the money on the extra 3 percent performance.
For video editing - get a stable motherboard (an intel 850 chipset should be perfect), RDRAM and a Pentium4 in the 2.5 Ghz range. Also make sure its a 533 FSB Pentium 4, not a 400 Mhz.
Spend the extra money on the best, fastest hard drives (a RAID setup may interest you although i dont have personal experience) and smile with a comfortable, reliable and fast system.
<font color=red><b>We highly recommend Intel's P4 processors.</font color=red></b>
We feel that these systems offer you the highest level of performance and compatibility. We've found that our cards are easier to install on a P4 based system. Intel has also added a bunch of special performance enhancers to the P4 CPU and it's chipsets that give it outstanding performance for video editing.
Video CODECs and non-linear editing software are being optimized for these new processors. Not only will they give you better performance, but they will encode dramatically faster into MPEG2 for DVD authoring and the various streaming CODECs. The latest P4 CPUs and chipsets (2.2 Ghz+) are so fast and optimized for multimedia that they are outperforming some dual Athlon Systems!!
They also go on to say some good things about Athlons. If video editing is going to be your primary purpose, I suggest reading a lot of what they have to say. They've been at it for years. They also have good info on the other hardware you might need.