After installing the Speak Window version 4.30 or 4.40, you will need to associate any .EN file to the Speak.exe so that all .EN files will open using the Speak Window.
Instructions for Setting up EN File Association for Dectalk
By Blake Roberts

Important notes: In order for Dectalk to work on your computer, it must be in a folder on the c: drive. That means Dectalk must be in, for example: a Dectalk440 folder when you open up the drive's contents, not in a subfolder. For your convenience, the zip file has all Dectalk files in a Dectalk440 folder. To make things easy, extract the zip file to your c: drive.

The following steps refer to both menu items and the associated keyboard shortcut, whenever possible. This is so that keyboard users, like myself, can follow along with mouse users.

1. Go into the Dectalk folder.
2. Locate an EN file. Right-click on the EN file. Keyboard shortcut is shift-f10.
3. Click "properties". Keyboard shortcut is r.
4. Click "change". Keyboard shortcut is alt-c.
5. If you see "speak" in the list of programs, press enter on it. If not, proceed to step six.
6. Click "Browse". Keyboard shortcut is alt-b.
7. Locate speak.exe in the Dectalk folder on your hard drive.
8. Click "OK". You will probably have to click OK twice.
9. To make sure the EN file association was set up correctly, launch demo.en.