Its really just about practice. Any good player can do well with any mouse and DPI. Your DPI and mouse are personal preferences, not main factors for succeeding in BC2.
I know there are multiple YouTube videos on BC2 about how to improve your game. Watch and implement what tips they offer. I personally found this video very enlightening: http://www.youtube.com/watch?v=0p4fkH9qC4M
This game is not a total run n' gun type of play, but you can occasionally get away with a little bit, but dont push it.
Also, learn to burst fire, it will yield a LOT more kills than if you don't. And kills are good