He might have a 775 Quad-core processor. That should support a GTX660Ti.
Yes, but it will bottleneck it. Even newer Core 2 Quads from 2009-2010 bottleneck modern graphics cards.
I reckon an overclocked Core2Quad shouldn't bottleneck a GTX660Ti.
It definitely can support it, but it wont perform as well as under a modern quad core CPU.
Of course. But he doesn't necessarily need to upgrade his CPU/MOBO just yet.