Can you supply some info on what happens when you try? I was successful at installing the Windows 7 version on Windows 8 as well as Windows 10 Tech Preview by just right-clicking and choosing to "Run as administrator" with no errors on both platforms.
I was also able to add the M20 by clicking the Start Menu and typing Scanner then choosing View Scanners and Cameras and adding a new device using the new driver installed in C:/Windows/Twain_32/Xerox/Xerox Workcenter M20 Series