Processor. More RAM will make it possible for you to open bigger files. Hard disk has no role in rendering, possibly just in opening, if any program needs to use Virtual Memory. Memory speed influences the speed at which programs work in ordinary tasks. BTW, the nominal processor speed has nothing to do with the motherboard. The only problem you might have with that is that your motherboard cannot support a higher-speed processor. Finally, if you have any other program opened and working in while you're rendering, it will influence your rendering time, because the processor has to split its cycles between the programs.

-- erlik