Dual Core vs Core 2 Duo

How big a difference is there between a dual core n a core 2 duo processor clocked at the same speed… in terms of performance??? Any idea ???

According to Wikipedia, Core 2 Duo is the commercial name of one of the model series by Intel, dual core would be the generic term that applies to chips made by Intel as well as others:

???
my friend (he owns a comp store) once said that :
Coreduo/Dual core = intel Pentium4 * 2
and core2duo = coreduo/dualcore * 2 / Pentium 4 * 4
???