Stupid preloaders!

hey guys! i really need help making a preloader. i thought it would be simple. ive looked at several tutorials, but nothing is working right. i have an animation that i want to be the preloader. i just want the animation to play as the bytes are loaded. i only want it to play once, not over and over until the file is loaded. so basically i need it to play at the same time, proportionally, that the bytes are being loaded at. does anyone know the actionscript for this? your help is much needed. thanks in advanced!