Hmm, Core 2 duo IS dual core technology. There is none that is better as they are the same, although there are different types of dual core processors such as Core 2 Duo and Pentinium Duo (It's called pentium dual core) or core 2 quad processors. ( core 2 quad is a little bit trickier.)
Way to confuse him...
A dual core processor has two CPU cores... it's kinda like having two CPUs in one. There are many on the market.
Core 2 duo is the name of a CPU that intel produces. It is a dual core.