- nforce4 ultra main board(msi neo4 platinium).
I don't know this chipset so I can't help here.

- nvidia geforce 6200 turbo cache(32 MB) graphic card.
Nvidia cards are generally a good idea for a linux computer. 3D acceleration of the nvidia driver for linux is much better than with ATI (for 2D you won't even have to install new drivers).

- LCD 17"(1280x1024 or 1024x76 monitor(new Hyundai L70D(DVI in) or Philips 170C5BS(DVI in)).
no problem

- Two sata segate 7200.7 barracuda drives
Hmm, I'm not sure here. In principle yes, but it depends on your sata controller (not on your drives). I'm not an expert here, so maybe someone else can help.

- Athlon-64 winchester 3000+.
- DVD-R/+R burner NEC 3520
- DVD reader NEC 5800
Should be no problem, no problem, no problem... But I've heard that kanotix (similar to knoppix) supports Cool 'n Quiet - perhaps you try this distri, too