DDR or DDR2

Hello all,
I am considering to upgrade my computer (which is a 754 athlon 64 3700+ and a 
k8v motherboard) to an amd 64 939 platforms, and I would like to know which 
direction shall I take.

which of nforce[3,4] and via chipsets for fedora 64 bit is best supported?

My main use of this computer will be computations that sometimes require large 
memory, simulations and also graphics.

Regards;
Mohamad Al-Saqer