All tutorials are included in the SmartOpen help file
Tutorial 3: ??_ compressed files
Introducing advanced conditions
In this tutorial we will be using the Unknown special extension to associate all unknown filetypes with SmartOpen, then instructing it to open those with a three letter extension ending in an underscore with WinZip.
For this tutorial I will assume you have read Tutorials 1 and 2. First add the new unknown extension to SmartOpen, and add a *.??_ condition to it. Add to this condition a new action Open With WinZip, with the command line c:\program files\winzip\winzip32.exe %1 substituting for the path where you installed WinZip. We must also, however, consider what should happen to the other unknown files. To deal with these, add a new * condition to the unknown extension, and give it an action. The command line to use for this action is largely up to you. You may decide to have unknown files open with notepad, quick view, or some other general purpose file viewer or editor. If you want to display the default windows "Open With" box (horrible though it is), then use the command line rundll32.exe shell32.dll,OpenAs_RunDLL %1 exactly as written here (copy and paste it). This can be inserted automatically by pressing the browse (...) button next to the command line box, and pressing the (Open With) button.