dell dimension 9200

I have a Dell Dimension 9200. I know its old, but i know there's ways to make into a lower end gaming PC. I upgraded to windows 7, computer has 4gb of ram, a geforce 7900 gtx and a 1tb HDD. Beyond popular belief, i have read you can upgrade to 8 gb of ram and up to an intel core 2 Extreme Qx6800...