You can use the same plugin for Opera that is used for Netscape.
The path to the demoxplug.exe is an older path that was used when the DemoShield 6.0 version was first released. The demoxplug.exe is created with your DemoX distribution. To ensure the file is found and that the correct version is being used, it would be best to direct the path to the file on your server.
The double slash that appears before the filename is most likely a result of the path that is entered into the Web Server URL field when running through the Distribution Wizard. You do not need to add a slash at the end of the path.
Also, you mention that you are using DemoShield 6.00. I would recommend making sure you have the latest update for that version. You can download the latest maintenance release for DemoShield 6.0 from the following URL:
The latest update for DemoShield 6.0 can be updated to version 6.03
All the best,
DemoShield Technical Support