I'm supposing that you're trying to find the difference between the Intel Dual Core and Core 2 Duo. The Core 2 Duo is a dual core, however, the Intel Dual Core is actually called the Intel Pentium Dual Core, and is a lower end processor compared to the Core 2 Duo.
I assume your question is "Whats the difference between a Pentium Dual Core and a Core 2 duo. Depends on what models your considering but the two biggest factors are fsb and cache. Also the newer Pentium dual cores are 45nm while the older C2D's are 65nm.
Just like the Athlon for AMD, the pentium name has become their "budget" model and has nothing to do with netburst, though there were some pentium netbursts for socket 775 when it first came out including a dual core (called "pentium D"). But the newer (2007) "pentium dual cores" are based on the core 2 architecture.
There is even a "pentium" for their new socket 1156 (Pentium G6950), and it is based on the core i architecture. Just like AMD's new Athlons are based on the phenom II architecture but have some things removed for the budget crowd.