Configuring Windows Explorer
Registry Overview - Additional Keys

This page lists some special keys found in HKEY_CLASSES_ROOT.
HKCR is an abreviation for HKEY_CLASSES_ROOT
HKCR\CLSIDThis is what makes OLE work
HKCR\FILETYPEContains pointers to various CLSIDs
HKCR\FilterContains pointers to various CLSIDs
HKCR\MIMEAssociates MIME types with file extensions and CLSIDs
HKCR\QuickViewContains a key for each extention known to QuickView
HKCR\TypeLibLots of CLSIDs
HKCR\UnknownProvides the Open AS... dialog box for un-registered file types
Adding key/command provides a menu selection for all un-registered file types
Must use RegEdit to modify values

Have fun.