[stansdds]

I have the Core duo E6850 3.0 Ghz but have never tried to overclock it....do you need extra cooling??

It really depends on how much extra heat is generated by the overclocking. I had a e5200 which ran a stock speed of 2.6, I had it running at 3.2 with less than 5 degrees increase in temperature under load - on the stock cooler. The coolers which come with the modern intel CPUs are very good, but decent air flow through the case is highly recomended.

On my new laptop I will have a core 2 duo processor (t6400) running at 2ghz per core. Will I be able to overclock this?

I've not tried overclocking a laptop. I would think that cooling could very quickly become an issue with a laptop.