Taken from PC World Magazine, December 2011 Edition

You can easily change the program associated with a particular file extension. In Vista or Windows 7, right-click a file of the type you want to reassociate and select Open With -> Choose Default Program. Double-click the desired program. In XP, right-click an appropriate file; select Open With -> Choose Program. Check always use the selected program to open this kind of file. Double-click the program. If you can’t find the right .exe program file, keep the dialog box open as you click Start and look in the Start menu. Right-click the app’s shortcut, and pick Properties. On the Shortcut tab, select the contents of the Target field; press <Ctrl>-C to copy to the clipboard. In the Open with dialog box, click the File name field; press <Ctrl>-V.