App-or-applet Alerts Download Stream Stoppage

I'm building a script that's 90% complete. It can download almost any file without
human eyes watching a monitor. I need one last piece to complete the puzzle.

A single purpose applet that can monitor the download stream of a popular manager
like FlashGet. If the bytes stop streaming for a certain period of time (maybe 30
seconds) a dialog box created by me (or the applet) will launch. It doesn't have
to be a dialog box. It can be any file, window, etc.

I would be happier with an applet, but any "resume download" manager that would
wait a specified period of time after the stream stops and pop-up an alert message
would be ok too.