Just doing a quick search of the Processor module part on a used Dell parts page, it appears those are server processor modules and likely won't even fit into your C600. As an add-on to that claim, it's not like there are twenty mobo upgrades for ANY laptop you can buy, let alone one - so that's your only mobo, and that's probably your only CPU [750Mhz]
I have the same model, and I'm more likely to head back to Dell Auction or Dell Outlet to get an updated model on the cheap with more stuff and nicer parts and configurations than purchase parts for this particular mobile unit. You can clone the HDD over to the new(er) HDD of another laptop and keep on scootin' without losing any data or having to reinstall all your stuff if you're a stickler about keeping things the same, but I suspect you'll find all this out soon enough. I believe that production model is more than at its' end.