Do a search for the game and then pick which platform you have it on (Not really necessary) You'll find a load of walkthroughs that tell you how to get through the game.
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The hundred billionth Crayola crayon ever produced was Perriwinkle Blue
The key to beating the helicopter is timing. You have to be able to time when you run out from behind a corner and shoot at it when it makes a second pass. However you can't be out from behind the corner when its shooting. You'll never make it if you do.
I haven't played that game in months but that part of the game sticks in my head some what due to how long it took for me to beat.
Now from what I remember doing, you must hide behind the wall pillars in order to protect yourself from the shooting. Then as the shooting has stopped you take aim from the side wall and fire your weapon. Now it might take some time, you might have to figure out the path of the copter in order to get it right, or it just might take some ammo to distroy the copter.
Either way you most likely won't get it done right away after reading this but it should be of some help.
If this doesn't seem to help I'm sorry because I'm not to fond of remembering how exactally to beat that part and you might be better off checking out the site mazman had suggested, but good luck anyhow.
yeah, it makes for progress if you just cheat past that one part. And then you can go on and maybe come back to it later. At least thats what I do. I have to go back so my conscience feels better.
There isn't really anything wrong with cheating. All it really is is a short cut for video games when you don't want to take the long road to the end of the level.
Go for it Whiiite_Diamond cheat your way to victory.