There is no Windows 7 support from Umax for this scanner model. It's only supported in the OS's listed below:
Astra 5600/5650 PC Driver
Windows 2000 (<--- will also work in Windows XP)
Due to the large size of the file(s), it's advised to save the file(s) onto your computer, then proceed with the installation.
Download link: (50.3 MB.)
Or you can get links to this driver in this thread: http://forums.driverguide.com/showthread.php?t=41320