I have a Intel Core 2 Quad Core Q6600 2.40GHz PC with a ATI Redeon 5670 HD. It plays most games on high settings but a lot of the current games only run on medium settings. I would like to build a new rig but money is tight. Can I get away with just upgrading the graphics card? I was considering a gtx 670. Would just upgrading the graphics card fix my issue? I would like to play most if not all games out right now on max settings. Is my computer even capable of handling such card? Any advise would help thanks.

Yes you can get away with just upgrading the card right now. Actually. I have to say wait until Nvidia releases the 660. It wont be that long of a wait and I hear that ATI are prepping a major price reduction in response.

Yeah, I'd wait for the 660. It's out this week if all goes according to plan, but expect limited quantities. Your processor will hold back the card a bit, but not to a larger degree.

Your card is definitely the bottleneck, but your processor isn't very far behind.