Your cpu is causing a major problem with your system. You need atleast a 2.7-2.8 oc to not hold your card back too much, also dual core would help. Also that mixed ram setup you have will cause you not to run in dual channel, I recommend a matched 2x1gig dual channel kit, as games are getting very ram dependent. Edit also by the looks of it your stuck with socket 754, a cpu/mobo/ram upgrade would really benefit you, your current system is a major bottleneck to your gfx card.