I am going to go against my normal recomendation of AMD based systems.
There is 1 thing that the P4 does do better than the AMD Athlon's, and that is video editing.
Since 3D animation involves active video, a P4 based system will likely be worth the extra cost.
Specifics:
I recommend using Intel motherboards with Intel CPUs. They just work very well together.
Get one that uses DDR RAM as it benchmarks faster than RDRAM.
If this is for gaming, go ahead and get a Creative sound card.
If not, I would get the Santa Cruz from Turtle Beach.
Video, I have a hard time choosing between the latest ATI and Nvidia offerings. In this instance, I would likely lean towards ATI.
Start out with at least a 500 Watt power supply. You are going to be running this thing hard, and need all the power you can get.
The rest boils down to personal prefference.
Since your market is likely not a 'business' application, I would go with XP Pro for your OS.
Yhat way, you can installas much RAM as the motherboard and budget allow.
Chas