Quote - > Quote - Memory speed shouldn't matter as much as in the raw processing of the chip.  While I love my X2 if I was buying a new box right now I'd look at a core 2 duo or the quad core, well its' 2 c2d cores glued together but thats another debate for another time, one depending on your budget.  

That's exactly what I've heard about the new quad core CPU, it's a 2x2 cores and not a true quad core, may be a while before Intel introduce a true quad core CPU.

So if the raw processing speed of the CPU matters, what about the Pentium 4 3.0 Ghz and above?
Does overclocking of CPU helps?

What about the performance of video cards, do they matter in regards to the rendering speed?

No the core 2 duo's are a much better generation of processors over the old P4 cores.  Far more efficient than the old ones were.  They are to the point where i'd consider buying another intel system again and i've used amd's for the past 4-5 years with a X2 as my current build.