I just learned about the possibility in a book I am reading and thought I would pass it along either for you or future readers looking for a way to show a popup from a shell script. This site shows it well:

http://techibee.com/powershell/how-to-get-pop-up-message-box-using-powershell/839

Granted, PowerShell is not setup by default (and arguably should never be) to allow double-clicking a script to invoke the execution of it the way Windows Batch us for security reasons but the code solution itself seems more elegant and wscript can be called from a Batch script just the same.