How to Change Image Viewer File Associations in Windows Vista

To edit the registry, first back it up, then do the following:

1. Open your favorite registry editor and navigate to this key: HKEY_CLASSES_ROOT \ SystemFileAssociations \ image \ shell \ edit \ command
2. Doubleclick the entry in the right pane.
3. In the data value field, type the path to the program you want to use (for example: "c:\Program Files\IrfanView\i_view32.exe" "%1"

You can change the editor for a particular file type this way:

1. Click Start Run
2. Type CONTROL FOLDERS
3. Click the File Types tab.
4. Select the file type from the list and click the Advanced button.
5. Click New.
6. In the Action box, type Edit
7. In the Application Used To Perform Action box, type the full path to the application you want to use to edit pictures.
8. Click OK twice to close the dialog boxes. This sets the default image editor for the selected file type.