Could be the RAM, erm..I dont think the video card would struggle with that though, how much space have you left on yr HDD, might have something to do with lack of space on yr HDD, are you in a position to reformat? A good old spring clean will defo fix it.
Right, im just reformatting a pc now, quite good specs with a card lower than that, ill put the game on and see what happens. Ill let you know. the specs for the pc are i think