The most reliable way to use an unsupported scanner like the UMAX Astra 5800 on 64-bit systems is via VueScan .
Some users have had success "spoofing" the driver using files from the Astra 6700 or similar models. Locate the file from a Vista 64-bit driver of a similar Umax model. Manually update the driver in Device Manager Umax Astra 5800 Scanner Driver For Windows 7 64 Bit -UPD-
The SANE (Scanner Access Now Easy) project includes a backend for Umax Astra scanners, including the 5800. The most reliable way to use an unsupported