The Folder Options dialog in Windows XP Explorer had a File Types tab that allowed one to change a file type's icon. Windows 7 doesn't have this. Is there a way to change file icons without changing its default application?
I recommend Default Programs Editor for this task- it's designed for Windows 7 and makes it really easy to edit that kind of stuff.
Check it out:
You can refer to a tutorial on how to use FileTypesMan to change file icons, or you can manually edit the registry.
(FileTypesMan can be downloaded here.)