A lot of older hardware lacks driver support for Vista and Windows 7, if the XP drivers fail to load, and fail to work, and if you cannot locate a suitable driver, then you might be out of luck and have to purchase a later model scanner. Later model "All in One" Printer/Scanners can be purchased for around $50 for the cheaper models.
I know that when I took the step from XP to Vista I had to get a new scanner.
See if these are useful.
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http://www.visioneer.com/company/contact/
Updating Your Scanner Driver