ah, as for installing it.. if you know how to get to the device manager, uninstall the current scanner driver from there and reboot, then it should look for the driver and point it to wherever you extracted the files to
i assume you tried the new benq drivers... those didn't work for me before either but for some reason do now.. i uploaded an older driver set that should hopefully work.. they are from when it was still acer and not benq, and they worked for me when i had your same problem. if i remember this driver set is version 3.40.. good luck!
http://sio.midco.net/ack/320u.zip ~1.5 megs