Sir, difference between Core 2 Duo and Dual Core is *I think* the fabrication process and the fsb.
Core 2 Duo is more recent than Dual Core pero may mga lumalabas parin na models ng Dual Core, albeit on lower end processors like Celeron.
Mga mas may alam po, paki correct nalang ako. xD
If you don't mind going AMD, I would suggest an Athlon II with an AM3 board if ever you want to still upgrade your processor to a Phenom II. Anyways, I haven't looked up much of the current items to date so I can't give a full spec recommendation, sorry. Dx