I had the same problem with the Microtek ScanMaker 4900, here's how i solve it.
after i installed the software and driver for my scanner on a windows xp machine i used a program called "double driver" to make a backup of my drivers on the xp machine and i only selected the scanner driver in the list for the backup and unselected everything else, all these in the double driver program, then i selected the output folder to save the backup and then i copied the backup to the memory stick and then on the windows 7 machine plug the scanner and it won't be recognized well, just go to the device manager and on the scanner with a question mark or exclamation in your scanner right click on the mouse and select update driver, now go to the path on the folder in your memory stick where are located the driver files of the backup that you did before on the xp machine and that's it, all u have 2 to is installing the software that controls the scanner.
it worked 4 me, i hope this works 4 u
grettins from México