Page Load Progress Indicator

Many times when building an application we need to load/unload a page into the browser to display new info.  With classic ASP (which is still alive and kicking) it's very hard to create a pre-loader that provides a visual indication that a page is still loading, or better, that a script is still in progress.  It would be great to have an extension (most likely using AJAX) that allows you to specify a progress indicator (and style) and a way to allow a progress indicator to appear while a page is loading or script is running and then automatically clear the progress indicator when the page has loaded or script has completed - In short, similar to a progress indicator you see when a video is loading into a media player.  Basically, this extension should work by adding it to a "main" page and then perhaps specify an IFRAME or <DIV> on the main page as the target container to hold the loaded contents; A button (graphic or actual) on the main page would then be specified through the extension's interface with a behavior that would "load" a page or execute a script - either of which could be dynamicially specified. This extension should work for classic ASP (and probably PHP to make it universally adaptable).