We had the same issue with our new Windows 8 OS and our old Xerox 510 Wide Format
You must DISABLE the Windows 8 Driver Signature Enforcement to use some of the Xerox drivers.
Do the following:
Windows Key + R (brings up RUN command)
type in shutdown.exe /r /o /f /t 00
Click OK
Windows will Restart
Select "TROUBLESHOOT"
Select "ADVANCED OPTIONS"
Select "WINDOWS STARTUP SETTINGS"
Click RESTART
System will restart to "Advanced Boot Options" screen
Select "Disable Driver Signature Enforcement"
System will start and you can install your printer with the appropriate driver.
Good Luck!