HKEY_CLASSES_ROOT\OggFile

This is where you set icons... DefaultIcon

HKEY_CLASSES_ROOT\Media Type\Extensions\.ogg

This is where you register source filters

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MediaPlayer\Player\Extensions\Descriptions

Register to appear in media player drop list... three keys here.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MediaPlayer\MLS\Extensions

Special support for media library.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Multimedia\WMPlayer\Extensions\.ogv

All sorts of crap for wmp 9 + and media library

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Multimedia\WMPlayer\Groups\Video\OGV

grouping for media library

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Multimedia\WMPlayer\MIME Types\video/x-ogg

MIME Types