Visioneer doesn't have Windows 7 (or Vista) drivers on their website for the 8700 so it might not be compatible. Two things to try:
With the scanner plugged into your computer and turned on run Windows Update, that could get compatible drivers.
If that doesn't work, download the XP drivers from their site and during the install process run them in compatibility mode. Sometimes that works, sometimes it wont. Note: their site says to use XP SP1.