Click start->Settings->Network and internet->Sharing options->Turn on file and printer sharing
You must change your permissions under the Sharing tab to include everyone and give read write access as needed. Also go to control panel->Network and Sharing Center->Advanced sharing settings. click All networks. At the bottom of the drop down select Turn off password protected sharing.
Another approach:
This keeps the "owner" in control of their data.
- first, a folder is owned by user X
- user X Shares it
- now user Y maps that folder to his/her system
- and uses userX's password
This even works across system types {Mac, Linux, Windows}