Download the newest XP drivers from this german site: http://www.mustek.de/eng_/html/treiber/scanner_scanmagic_usb.htm
You will need the SN ofyour scanner (it is on the scanner).
Get the one file instalation.
You will not be able to install the drivers but you can trick them to work.
The procedure is simple:
Do not plug in the scanner, start up the
Empty your systemroot\windows\temp folder
Srart the instalation and when it asks "Select Language" stop there. Then copy the all contents (files and folders) of Windows\Temp to another folder (e.g. systemroot\1)
Then plug in the scanner and windows should be able to find the drivers there if not guide it to that location and let it install Mustek Twain drivers.
Enjoy your scanner. :-)