I couldn't find anything about Myopoly8 and its availability. There are also no updates or certain information to specify if the software can be used anymore. Due to the lack of these updates, I believe that Myopoly8 is now a discontinued application. If you still have the installation package, then make sure you don't lose it as it's the only version available that can still be used.
Secondly, to attempt a possible installation on newer versions of Windows, right click the file and then go to Properties > Compatibility. Choose a previous version of Windows and then launch it again.