The Dink Network

There's HKEY_CLASSES_ROOT in the registry, with which you can setup the file's type to show in the explorer. I'm searching through regedit now for the place with the keys that determine which program to open these files with.

EDIT: http://www.codeguru.com/vb/gen/vb_system/directoriesandfiles/article.php/c4837/#more might help.