Close all the application in vb.net

Here is an article focused on closing instances of a specific application, seems like you could rewicker it a little bit and close them all (including yours).  You may just consider throwing up a message box and telling the user that you recommend closing all open applications instead of shutting them down without their consent.  Just a thought.

The article mentioned is here, I hope it helps:

http://support.microsoft.com/kb/305602