If you are a gamer, the 560ti upgrade alone will make a huge difference for you. Even with the old C2D processor holding it back a tad. What resolution is your monitor, btw?
If you still want to upgrade the processr on that DDR2 motherboard, you'll probably have to look at used C2Qs on someplace like ebay. But if you want to go for a new processor and a new motherboard/memory investment, let us know what your budget is. There's no sense recommending a $600+ combination if your budget is 1/3 that.