You may get VirtualBox failed to open/create the internal network when you start a VM on Windows. The suggestions in this post are sure to help you.

The VirtualBox GUI and command line tool makes it easier to work with virtual machines and appliances. Find out how to get and use this open source virtualization tool.

You can open Cmd, a traditional DOS (disk operating system) style command line, the newer Windows PowerShell environment or use a terminal emulator to connect to a command line on another computer.

Figure A Creating your shared folder in VirtualBox 6.1. This will open your host’s file manager. Navigate to the newly-created (or chosen) folder and select it.

If you want to try Windows 7 out, but you don't want to wipe your current operating system from your system, then perhaps you want to try Sun's VirtualBox virtualization software.