I was asked by my good friend Adam Cogan from down-under how to change the HTML Editor that Internet Explorer uses for the Edit Button in the Toolbar. 

It seems that the list is the same as when you right-click (see image below) on the file in Windows Explorer and select "Open With."   More details on adding Editors (or any editors for that matter) at MSDN's Internet Explorer Client Registry Layout, also included below.

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.

1. Register the friendly name of the HTML editor by adding a new key to HKEY_CLASSSES_ROOT\.htm\OpenWithList.

   HKEY_CLASSES_ROOT\.htm\OpenWithList\friendly name

2. Add shell, edit, and command keys to the editor's registry entry.

   HKEY_CLASSES_ROOT\.htm\OpenWithList\friendly name\shell\edit\command

3. Enter the fully formed path of the .exe file that launches the editor in the command key's "Value data" field. Enclose the path in quotes if it contains spaces. The following example shows the Value data entry for a typical installation of FrontPage Express. Include %1 as a parameter. This parameter refers to the file name of the active Web page.

   "c:\program files\microsoft front page express\bin\fpxpress.exe %1"