I'm assuming you are using a PC and not a Mac. If you are using a Mac... nevermind! VBG
Go to Windows Explorer or the Control Panel and do the following:
Click on TOOLS --> Folder Options --> File Types
Now the tricky part -- you need to know the 3 digit file extension for the files you want to change (like MP3 or JPG....) Scroll down the list until you find it. When you select it, in the bottom half of the dialog box it will show you which application is set to open ALL files of that type (with teh same extension). You may then click Change and change it to another application to be the default application set to open ALL files of that type.
Be careful as you do this -- for if you assign an application that is not designed to open that file type -- NONE of those files will open appropriately. You can go back and do the same thing to correct it... but in the meantime you will end up with "garbage" files.
I hope that all makes sense... if not please post back.