Windows Vista does an admirable job of determining the proper program to open a file with; however, it isn't perfect. The system automatically creates file associations between specific extensions and programs. You can modify or change this to create your own association. This is helpful if you want a music or video file to open with a specific media player; the same applies to any other file type.
Click on your "Start" menu and access "Control Panel." Choose the subheading "Programs."
Click on "Default Programs," and then choose "Associate a file type or protocol with a program."
Wait a few minutes for the file extension list to populate; the system searches for all file extensions on your computer.
Browse the list to find the file extension you want to create an association for. The list is in alphabetical order, by default.
Click on the file extension, and choose "Change." Click on the arrow to expand your program selection; if you do not see the program you want to use, click "Browse" to find the program.
Click on the program you want to be associated with the file extension; click "OK" to save the association.