Core Duo is the first "Dual" born processor from Intel and it was a quick reply for market in the concurrence with AMD.
In fact is a single processor with two levels of cache.
It is a 65nm processor,so a big energy consumer,involving higher heat,despite the name,it is not a Dual Core.
IntelCore 2 Due is different,is a 45nm processor with a very good resources management,and does in fact have 2 processors with separate cache.So this is the better one.