In this Macromedia Flash tutorial you will see how easy it is to make a flash preloader. In this preloader we will do a very basic animation while loading, but it can easily be turned into a more advanced preloader.

1.
A basic preloader contains 1 part with a small animation that runs while the rest of the flash movie is loading.

Now start by making an animation from frame 1 to frame 11 as I did below.
I just made a text saying loading, and for each frame I added a dot to indicate progress.

2.
Now make a new blank keyframe at frame 12, type in "done" or put in the movie that your flash has been loading.

3.
Go back to frame 11, and open the actionscript panel, and now we are ready to type in some code.

First of we need to save some information in some variables, total_bytes should contain the correct file size in KB
And bytes_loaded should count the amount of bytes loaded.

total_bytes = getBytesTotal(300) //write in the correct file size
bytes_loaded = getBytesLoaded();

Now we will make an if condition, that says if total byes - bytes loaded is more then 0 then keep on loading, else go to next frame, so we can start our application/flash movie.

if ((total_bytes - bytes_loaded)>0) {
gotoAndPlay(1);
}
else
{
gotoAndPlay(nextFrame());
}

And we are done.
Remember not to make a preloader on small flash movies, because they will load so fast that you don't even see the preloader. (as mine did).