Though this may not even be close to the problem, what I would suggest is checking the video card fan. If it's been a really long time since you've used it, it could have easily accumulated a lot of dust, which could KILL your cooling. Most NVIDIA cards reduce clock speeds when they get too hot so they can cool down a little, so that could just possibly
be your problem. It really does sound like a graphics problem; as your processor looks great, and your RAM is pretty good for BF2. I'd invest in a better video card if you can't find out what's causing this. Like a 7900GS
for $200, or a X850XT
for just $120. Of course the 7900GS would be better, but if you're on a relatively tight budget the X850XT is a pretty close follower.
If this doesn't fix your problem, I'm sorry; excessive dust would be my best guess. If you've got something to monitor the temperatures of the card, you can do that before checking the fan. I just think it might possibly be overheating.