Choppy frame rates = graphics most likely.
Update your graphics drivers to the newest ones... download them from Nvidia.
BF2 likes its RAM. 2GB is the sweet spot for the game. BF2 is also rather stingy... don't run anything else in the background besides your AV and such (TeamSpeak/Vent is fine, but not much else). You can try adjusting your in-game settings down some. I use the ones I posted in this post: What online game is best?
They are not eye candy, but allow you to see the other guy better. My card can run it full out, but I use these settings anyway.