There's nothing in windows that can share a scanner.
Some scanners can be connected directly to the network, and accessed
remotely. For example, our large Canon photocopier / printers are also
network scanners. They can also scan into a remote server shared folder.
Some domestic grade scanners may provide software which does this,
and there are a few 3-rd party utilities too.
For example:
http://www.remote-scan.com/download-free-client.php
In practice, remote scanning is not that great. You still need to walk to
the scanner and insert the document, then walk back to your PC to run the
scan, then go back to the scanner to retrieve the document.
A good way to do what you need is to have the scanner hooked to one machine
and configure it to scan into a shared folder which can then be accessed by
all the other machines.