Dual Core:
Intel produced a computer processors series with two processor chips is called Dual Core. In simple words it is power of two processors in one. They are cheaper and slower than Core 2 Duo processors.
Core 2 Duo:
Intel advanced their dual core processors technology with improved clock speed and larger cache are called core 2 duo processors. They are a little more expensive and faster than dual core processors.
There are more advance processor technologies available now.