I HAVE A DELL OPTIPLEX GX260 AND IM LOOKING TO UPGRADE MY VIDEO CARD. DO TO THE FACT ITS POWER SUPPLY IS LIMITED I HAVE A LIMITED AMOUNT OF CARDS TO CHOOSE FROM. I AM CURRENTLY LOOKING AT THE ATI RADEON 7500 32MB (WHICH I KNOW WILL WORK) AND THE ATI RADEON 7500 64MB (WHICH IM NOT SURE WILL WORK).WHAT DIFFERENCE DOES THE INSTALLED MEMORY MAKE AS FAR AS VIDEO EFFECTS? ALSO WHAT IS THE MOST AMOUNT OF INSTALLED MEMORY  MY SYSTEM WILL SUPPORT WITH ONLY A 180W PSU?