Finding a pre-built Windows Vista QCOW2 image for direct download is difficult because Windows Vista is a licensed operating system that Microsoft no longer supports. However, you can easily create your own QCOW2 image for use in virtualization platforms like Creating a Windows Vista QCOW2 Image
Step-by-step:
Always scan downloaded QCOW2 files for malware – they can contain pre-installed viruses. Windows Vista Qcow2 Download
This is the safest and most legal method, provided you own a valid Windows Vista license key. Finding a pre-built Windows Vista QCOW2 image for
Licensing: Even though Vista is "End of Life," it is not officially freeware. You technically still need a valid product key to activate the OS and avoid the "Reduced Functionality Mode." Windows Vista Qcow2 Download