i suggest you go for an i3 instead of a core 2 duo or core 2 quad, but if you can spend a little bit more, go for the i5 for the better. yes core i3 beats the fastest core 2 duo, because of the hyper threading, i3 is a dual core but performs like a slower quad core because of its multi treaded core.
i3 = 2 physical cores / 4 threads (Operating system reads 4 cores)
Qxxxx series = 4 physical cores / 4 threads (Operating system reads 4 cores)
Physical cores are actual ‘real’ cores. Threads are how many ways the data is transfered. Generally the number of cores match the number of threads but Intel’s new i3 have different amount of threads per cores which is called Hyperthreading. the faster core 2 quads beats the i3, but i3s are just close behind, thats the only advantage of the core 2 quads, they are a little bit faster, but there are alot of things that makes i3 better tan core2Q, like it runs cooler with 32nm, compared to core2quad's 45nm, less power means less heat and longer system life, another is i3s supports up to 16gb ram, core2s can only supports up to 8gb ram max. the i3 also has a built in graphics card, no need to buy a costly graphics card, so you save money. i3 also has a new architecture that will be the standard or all, sooner or later ill be a requirement for every processor.. the last is core 2 is old, and its retiring, core i-series are the new face of processors today and for years to come.