Dead easy.
It's probably best to put this in its own scene in your movie (add a scene in the Scenes panel, call it "loader" or whatever.)
Add three frames to your new scene.
1
//how much of the movie is loaded
loaded=_root.getBytesLoaded();
//how big is the movie
total=_root.getBytesTotal()
//is the movie already loaded?
if(loaded>=total){
//if so skip the loading process
gotoAndPlay(4);
}
2
No script but put a dynamic textbox with the variable set to "percent" on the stage, this is what displays how much of your movie has been loaded so far.
3
//check again how much has loaded
loaded=_root.getBytesLoaded();
if(loaded<total){
//if movie has not fully loaded
//work out how much has been loaded and display it in the textbox
percent="Loaded: "+Math.floor((loaded/total)*100)+"%";
//loop around
gotoAndPlay(2);
}
That's all you need for a functional loader - of course you can get way more complex. Slainte