Launch a program w/o user seeing confirmation dialog
You create an action button whose action is Hyperlink To, Other File --> an EXE or other executable file.
When you click this button, you get a dialog box suggesting that the program you're about to open might contain viruses and asking whether it's ok to launch it.
This may discourage people who are viewing your presentations from continuing. If they don't know you well, most right-thinking people will click Cancel, and that's the end of that.
Instead of using a Hyperlink action for the button, use a Run Program action instead. When you do this, the user won't see a confirmation message in PowerPoint 97, 2000 and the PowerPoint 97 Viewer.
From PowerPoint 2002 on, security got tighter, so this doesn't work as well. Links to external files won't work at all in the free PowerPoint 2003 viewer.