gosh i'm fed up of explaining this!! Its hard for a beginner to understand, so i'll try to make it as simple as possible.
Core 2 Duo - Older intel architecture, medium to high end 2 core CPUs, made on 45nm. Eg- Core 2 Duo E8400
Core i3 - Newer architectures, medium range 2 core CPU, with Hyperthreading, and made on 32nm. Eg- Core i3 560
Pentium Dual core - Low end 2 core CPUs made from anu of the above, by disabling some features, like cache, and lower clock speeds etc. Eg:- E6300 or G6950.
Generally speaking, "Dual Core" means a 2 core CPU.
Intel has confused 95% of PC buyers by branding some of their processors "Pentium Dual Core".
AND REMOVE YOUR PHONE NUMBER FROM THIS THREAD AS refillable SAID, USE THE EDIT OPTION ON THE LOWER RIGHT SIDE BELOW YOUR POST