Is it possible to have a button in a slide that can launch another file?

It is very easy to do this with PowerPoint and iSpring. On the PowerPoint toolbar, choose the "Insert" tab, then "Shapes" (or any other object you like), and then specify the hyperlink or any other external file for this button.

To add a hyperlink, right click on the shape you chose, click "Hyperlink" and specify the relative path to the file you want. Relative path means that the path should not be full and should look like "my_video.swf".

Now convert your presentation with iSpring.

Clicking the button you created will launch another file during Flash presentation playback. Please note that both the generated Flash file and the external file you linked should be placed in the same folder.