I've just seen a suggestion to check the Epson UK website for VISTA
drivers.
Here's their entry page for VISTA:
http://esupport.epson-europe.com/ViewFAQ.aspx?lng=en-
GB&ID=KB070001EN&data=22EF90957417DDBB2C76F17A441127E53333E27B1C3A5A6F9
8373BC06379405F
but that just indicates << Download available in January >> for a
listing of scanners including the 4990.
Here's a link to a VISTA version of their Epson Scan 3 software:
http://esupport.epson-europe.com/FileDownload.aspx?lng=en-
GB&ID=31731&data=22EF90957417DDBB2C76F17A441127E53333E27B1C3A5A6F98373B
C06379405F
EPSON Scan (3.0u)
EPSON Scan directly controls all of the features of your EPSON scanner.
With this software you can scan images in color, grayscale, or black
and white and obtain professional quality results. This program is the
standard cross-platform interface between your scanner and most
applications. You can access it from any application that supports the
TWAIN standard.
You will note that like other suggested solutions it uses TWAIN.
Good luck.