The Visioneer 8700 works with Windows 7 by using the 8900 XP driver:
From the Visioneer website, download the latest 8900 XP driver.
Right click on 8900.303113.EN and select "Troubleshoot Compatibility"
If you get the red-box warning that XP drivers aren't compatible, then you're good.
When it is installed properly, it will show up as "Visioneer 87xx/89xx USB Scanner".