To crash a helicopter you have two options: shoot the driver or ram it with your own helicopter. When shooting the driver aim for the right side of the glass when the chopper faces you. I would suggest a machine gun of some sort.
On Bridgetoofar, you can win easily if you start with three engineers, all get in a jeep (this only works with Chinese), and drive too the farthest base (2). Then one engineer gets out, lays some mines where the Americans will come from, and takes the base. Meanwhile, the other two are driving to base three (on top of the bridge). While one gets out and lays mines and takes it over, the final guy drives to base four, the closest one to the Chinese base, and does the same thing. You probably want to use your rockets instead of your shotguns, because there will always be guys driving up in tanks and humvees. Once you take the bases over, you just stay there and defend them. All three people will get lots of points, because you all take over a base, and you kill people that come to take your base. Then your mines will get you more points later.
If you play this game online, here are a few hints to help you out:
First, On the map called Bridge Too Far, be the chinese and get the rocket launcher kit and get in a jeep. Drive quickly to the American base, but stop on the ramp before you get to the base. Jump off the ramp to your right and go prone at the bottom of the ramp where it meets the fence. From there you should be able to shoot their jeeps.
Do you frequently use 120mm tanks? Tired of people puting C4 on you while you reload? Simply rotate the barrel and smack'em upside their head. If it hits, they will die! However, if they are crouched or proned you won't be able to hit them.