Calling For User's Attention From Background

The purpose of my application is to keep track of users waiting to use another application that may only be accessed by one user at a time.My vb.net application adds the persons name to the end of a text file, removes names when a person either gets to the front of the line or exits by closing my app.It regularly checks the list, and when the user gets to the front of the list, it notifies him and loads that other program.My problem is, I don't want the user to have to sit staring at my app until they get to the front of the line.I want the app to cause the computer to emit a regular, slightly annoying beep,even if the user has minimized my app or pulled up Microsoft Word on top of it, and continue to beep repeatedly until the user switches back to my app and presses a key or clicks the mouse.