very informative dude

can anyone tell me how to add the graphics of motherboard and that of graphics card?i am using asus m2n8 motherboard and nvidia 6200 turbocache 256mb graphics.....it is showing graphics as 512 mb without graphics card...after installing graphics card also it shows 512mb graphics....with only little improvement in performance....i have 1gb ram...processor is amd 3600+x2,dual core @2ghz...my pc is not performing well with games