Win7 when configured on peer-to-peer Network Win 7 has three types of Sharing configurations.
HomeGroup Network = Works only between Win 7 computers. This type of configuration makes it very easy to Entry Level Users to start Network sharing.
Work Network = Basically similar to the previous methods of sharing that let you control what, how, and to whom folders would be shared with.
Public Sharing = Public Network (like Internet cafe) to reduce security risks.
Since all your computers are Win 7 you can use the HomeGroup Network.
http://windows.microsoft.com/en-us/windows7/help/videos/sharing-files-with-homegroup
Home Network is very basic and lacks advanced setting. If you opt to use the Work network.
Make sure that the Software Firewall on each computer allows free local traffic. If you use 3rd party Firewall On, Vista/XP Native Firewall should be Off, and the active Firewall has to adjusted to your Network IP numbers on what is some time called the Trusted Zone (consult your 3rd Party Firewall instructions.
General example,
http://www.ezlan.net/faq#trusted
Please Note that some 3rd party Software Firewalls keep blocking aspects of Local Traffic even it they are turned Off (disabled). If possible configure the Firewall correctly, or totally uninstall it to allow clean flow of local network traffic.
When finished with the setting of the system it is advisable to Reboot all the hardware including Router and all computers involved.