Preloader in as3

i have three swf files that i load into a “main_file.fla” Using URLRequest and Loader classes,so i need a preloader(separated swf file) for the user interface that loads the " main_fie.swf"(that loads 3 files)and i want to be able to start the first two files at the same time on the first frame and the third file on the second frame of the “main_file.fla”,hope that you can help me ,i can upload my files if you need…a good tutorial can also be great.

thanks in advance