Will this boost up my pc performance

Ok, so i have this really good pc, and its RAM is 2Gb and it has a Nvidea G-Force 9400 video card, and i wanted to boost up its performance. I have a 2Gb memory card (from my old pc), so by adding it to my new pc will that make the RAM 4Gb. Also does having 2 video cards improve video game performance?