Sorry but your 9800 GT 512MB isn't very good for BFBC3.
Your CPU is also quite weak - X2 dual core at 3Ghz.
Try lowering your resolution - 1600x900 would be very taxing on your computer (due to your low specs). Bring your resolution down 1 notch and try again. BF3 is quite the demanding game, especially in the GPU department.