Yes, by now we should all know that Flash MX can load .jpg files dynamically into a flash movie aswell as being able to load external .swf files, but as always, when it comes to loading large files from external sources, it is good practice and almost standard to create a preloader for the file. The Flash MX Event Model may be causing you problems when it comes to preloading files loaded into your main movie using the Movieclip.loadMovie method or the loadMovie and loadMovieNum functions….
Simple Bar Preloader Tutorial
The idea behind this preloader is that we halt the progression of the movie and find out our filesize. We find then find out how much of that is loaded, use these numbers to create a percentage and then affect the scale of our bar to represent this.
Friendlier Flash: Creating a Flash Preloader
With the release of a new version of Flash, Flash movies on Web sites are more popular than ever. While such movies succeed in adding interactivity, animation, and information to a site, some Flash movies can become prohibitively large. After all, not everyone on the Internet has DSL or cable access. Keep in mind that many of your site visitors are still plodding along with dialup access. Although Flash does a respectable job of cutting down the size of movies for Web sites, they can still be quite large. This is bad news for your site visitors viewing your site through the aforementioned slow connections.