Every core 2 quad is good for gaming but most dont worth the money.Most games need frequency speed and not many cores thats why core 2 duo's are great for gaming.For example:Core 2 Duo e8400 vs core 2 quad q6600.
Core 2 quad: 4 cores 2.4ghz FSB 1066 65nm technology L2 Cahce:8MB
Core 2 Duo:2 cores 3.0Ghz Fsb:1333 45 nm technology L2Cache:6MB
The quad core CPU is a 65nm one where core 2 duo is a 45nm CPU whch means core 2 duo is better at that factor.
Core 2 duo has got 2 cores but core 2 quad has 4 cores,that means core 2 quad is better for multi-tasking(running a lot of applications at the same time) but core 2 duo is more efficient when running a certain application than core 2 quad because of its high speed.Although some new games take advantage of the 4 cores, most games do not.An other advantage of core 2 duo is its cheap price and its great ability for overclocking,as it can reach 4.2Ghz.
BUT! if you find a CPU with the same frequency as core 2 duo but with 4 cores then it is better.Thats why I recommended this quad-->http://www.newegg.com/Product/Product.aspx?Item=N82E16819115130
Final conclusion is that if you want to buy a core 2 quad you need to pay a lot of money but if you want to spend about 150-180$ then go for intel core 2 duo beacuse quads at that price are not better.
Something troubling is that intel stopped the production of core 2 duos and core 2 quads so it might be difficult to find them