Is dual core better than core 2 duo

it depends. intel dual cores range from pentium d's to the current pentium g630...
core 2 duo is slightly different architecture and in most cases is better but the g630 is a good dual that will out perform many core 2 duo's due to being smaller, more transistors and more cache.
but to be honest both are dead ends as far as gaming goes... most high end new titles need a tri core minimum and next year a quad will likely be the minimum or most high profile games.
the reason intel still produces them is there cheap and not entirely useless. after all you dont need a 4.5ghz quad to surf the web and write an email...