How Microsoft Vista stores default icons of certain file extension in the Windows registry

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\VLC.avi]

@="VLC media file (.avi)"

[HKEY_CLASSES_ROOT\VLC.avi\DefaultIcon]

@="\"C:\\Program Files\\VideoLAN\\VLC\\vlc.exe\",0"

Changing the DefaultIcon key is the way to change the icon :)