The following tip requires editing the Windows Registry. Be sure to make a backup copy of the registry prior to making any changes to it.

The "Open With" list can be found in one of the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileEx­ts
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\<<particular_extension>>\OpenWithList
HKEY_LOCAL_MACHINE\SOFTWARE\Classes\SystemFileAssociations\<<particular_extension>>\OpenWithList