It's time to bury the Umax. You can get a Canon LIDE 220 or 120 for less than you pay for a SCSI to USB adapter. It does require 10.6.8 or greater though. You didn't mention what version of the operating system you're running.
Besides costing less the new scanners have a much smaller footprint, and most of them don't require a power supply. It runs off the USB cable.