Core 2 Duo vs Core quad!!

I think I will upgrade my proccesor(P4 3.4)..I have saved my money, so..I think they are compatible with the motherboard cause in PC Wizard it says in the proccesor tab: Support LGA 775 so I guess I can fit them, right? I have seen these two:
INTEL CORE 2 DUO E6850 3.00 GHZ LGA775 - 1333 FSB - BOX
vs
INTEL CORE 2 QUAD CORE Q6600 2.40 GHZ LGA775 - 1066 FSB - BOX
One is quad but the other has more hz...What is better? The price is quite similar..Also what is whats the difference between 45nm and 65nm??
Cheers
INTEL CORE 2 DUO E6850 3.00 GHZ LGA775 - 1333 FSB - BOX
vs
INTEL CORE 2 QUAD CORE Q6600 2.40 GHZ LGA775 - 1066 FSB - BOX
One is quad but the other has more hz...What is better? The price is quite similar..Also what is whats the difference between 45nm and 65nm??
Cheers
