My s400 works with Vista but not Windows 7, I

It will work with win 7 but it is complicated.

Download driver from the Microtek website
extract the files to your drive
locate the setup.exe file where you extracted the files
after the driver is installed reboot the pc

Now for the fun part...

Once PC is fully rebooted plug in Scanner ScanMaker s400
Windows looks for drivers in “windows update” and the “preconfigured driver folder”
Windows cannot find a driver.
Close “Driver Software Installation” window
Open Device Manager
Device manager shows yellow bang next to “USB scanner” under “Other Devices”
Right click on usb scanner
click “update driver software”,
Click on “Browse my computer for driver software”
Click on “let me pick from list of device drivers on my computer”
Click on “Imaging Devices”
Click Next
Under Manufacture there is no Microtek
Click on “Have Disk”
Click on Browse
Locate ScanWizard 5 V6.63 folder
Locate Disk 1
Locate Vista
Locate X86
There is a list of INF files
Choose first inf file, “Mii_x86_004.inf”
Click Open
Click OK
Now under Manufacture two entries are listed, Microtek and Microtek Driver Team,
On the other side there is a list devices s400 is not listed
There is an entry for 4800 Scanner
Select it and click next
An “update Driver Warning” opens select yes
Window now shows successful driver update.
And the scanner is listed as 4800 scanner
Click close
Close device manager
Open Scan wizard program
Scanner works fine.
The scanner will not work nativly with windows scanning.

Unfortunately you'll probably have to shop for another scanner that's Windows 7 compatible. Please note that I've been repairing systems for 30 years and I can't think of any other reason.

BUT . . . . that doesn't mean someone else doesn't have a better answer so keep on asking. You're not alone in your search for drivers to run hardware on Win 7.