The "C" class are perfect for overclocking. They're really just 3Ghz chips sold at lower clock speeds and so will ramp up to 3Ghz without any trouble whatsoever. Just set the FSB to about 250Mhz and you're away, no need for vcore adjustments, extra cooling, nothing. There really hasn't been an easier chip to overclock since the Celeron 300A.
As for RAM, your existing sticks may work but then again they may not. Dual channel RAM works best if the sticks are matched performance-wise. Some chipsets, nForce2 in particular, are extremely picky about this but I wouldn't know how the Intel chipsets fare in this regard.