I've posted previously about using AutoIt to create balloon popups, e.g. for reboot notifications. NirCmd now provides an alternative way to do a balloon popup, in a simple tool that could be used in any scripting language of your choice.
Download NirCmd from http://www.nirsoft.net/utils/nircmd.html. You can see the syntax for doing popup balloons at http://nircmd.nirsoft.net/trayballoon.html.
Warning – these websites may be blocked by many companies, as NirSoft also contains many password related utilities.