How to set up Internet Explorer as default viewer for PNG files
in Win XP:

It is helpful for Ensign users to have the default viewer for PNG files as IE (Internet Explorer) rather than some other program (such as the default in XP, Photo Editor or Picture & Fax Viewer).

Run Windows Explorer and select menu Tools | Folder Options. Find in the Files list the PNG entry and click the Change button and select another viewer (i.e. IE). This image shows the settings used with the XP Home platform.