Yeah. An upgrade is the only cure. Dice is kind of like Crytech, they expect to punish your system no matter how good it is with their newest releases. As I understand it, BF3 is one of the few games out at the moment that is designed to take advantage of quad core processors. [Believe it or not, most games still only make use of 2 even at their highest settings.] The processor is the weakest link in your setup there. Add to that the fact that more and more games will be coming out that will make use of 4core systems, and an upgrade is the best option.
You won't be running on ultra, but you should be able to get a decent framerate out of medium to high settings with a better processor on BF3.