Windows 7 & Vista does not provide a GUI to dissociate file type extensions. But if you need to, you can do so using this portable utility.
- Download unassoc.zip from link mentioned below, and save to Desktop
- Extract the contents to a folder and run the file unassoc.exe
- Select the file type from the list
-Click Remove file association (User)
The user-specific association for the chosen file type is now removed from the registry. The system will now use the global file association settings.
The Remove file association (User) button Removes the user-specific association (via the Open With dialog) for the chosen file type. Note that this button will remain dimmed if there is no user-specific association for the file type.
The Delete file type button Deletes the file type completely from the registry. Both the user-specific and global associations for the chosen file type is removed.
And the Refresh list button, Refreshes the list box contents.
This utility requires administrative privileges to work correctly.
Download Unassociate File Types Utility.
Incidentally, you may also want to read about how one can set or change file type associations using the Control Panel in Windows 7 & Vista or about the Default Programs Editor for Windows 7 & Vista.