I'm sorry, you also asked about adding to the drop down list of programs for HTML Editor (other areas of Internet Options, Programs are handled differently).
Adding HTML Editors
The steps for adding HTML editors to the drop-down list on the Programs tab of the Internet Options dialog box in Internet Explorer 5 and later are slightly different than the steps for adding client applications like mail and news.
Register the HTML editor in the OpenWithList file type association of .htm files.
HKEY_CLASSSES_ROOT
.htm
OpenWithList
MyEditor.exe
Add shell, edit, and command subkeys to the editor's HKEY_CLASSES_ROOT\Applications registry entry. The "%1" parameter refers to the file name of the active Web page.
HKEY_CLASSES_ROOT or HKEY_CURRENT_USER
Applications
MyEditor.exe
shell
edit
FriendlyAppName= My HTML Editor
command
(Default) = "%ProgramFiles%\MyHTML\MyEditor.exe" "%1"
Note The edit subkey is required. If the FriendlyAppName value is missing, the application itself is queried for this information.
Close and reopen the browser for these changes to take effect.
Setting the Default HTML Editor
In Internet Explorer 5 or later, whenever the HTML editor is selected from the drop-down list on the Programs tab of the Internet Options dialog box, the Edit with... command on the File menu is updated to reflect the selection.
HKEY_LOCAL_MACHINE or HKEY_CURRENT_USER
Software
Microsoft
Internet Explorer
Default HTML Editor
Description= My HTML Editor
shell
edit
command
(Default) = "%ProgramFiles%\MyHTML\MyEditor.exe" "%1"
Note Applications such as FrontPage check this key to determine if they are registered as the default HTML editor.
Selecting a View Source Editor
By default when you use the View Source feature of Internet Explorer it launches Notepad as the text editor. The following registry key will allow another source editor to be used:
HKEY_LOCAL_MACHINE
Software
Microsoft
Internet Explorer
View Source Editor
Editor Name
(Default) = C:\Program Files\MyHTML\MyEditor.exe
Note Changes to this registry value take effect immediately. No environment variables (such as %ProgramFiles%) or command line arguments are allowed. The filename of the cached HTML file is passed as the first argument on the command line.