When I go to the Canon site, I get prompted to select my OS: http://usa.canon.com/cusa/support/consumer/scanners/canoscan_series/canoscan_fs4000us#DriversAndSoftware
However, this driver, fs4000usvst103ben.exe, is listed as a Vista 32-bit driver released in 2007. Since the 64-bit Windows requires signed drivers, Canon doesn't make 64-bit drivers for their older scanners. (This scanner was released with compatibility with Win98.) Thus you will probably get an error message about the unsigned driver when you try to install it.
If the driver refuses to install, you may be able to run the driver installer by using the compatibility mode. Download the file and save it to your hard drive. Right click on the exe file and choose Properties. In the Compatibility Tab, select Run this Program in the Compatibility Mode and choose XP. Click Apply and then OK. Right click again on the exe and choose Run as Administrator.
I hope this helps.