Enable the Guest account on each computer.
Tune Permission and Security to allow Total control by Guests and everyone.
Please Note that this metohd open evry thing to evryone. However, you can still restricted specific Computer/Drive/Folder to by specificaly tuning their Permission/Security.
http://windows.microsoft.com/en-US/windows7/Turn-the-guest-account-on-or-off
In general.
Permission and Security issues with Vista/Win7, check the following settings.
All users that are allowed to share need to have account on
all the computers that they are allowed to connect to.
Everyone is an account, it means a group of all of the users that already have an account and been established as users.
Using the
Everyone feature saves the need of configuring permission to each of the
established users, it does not mean
Everyone that feel that they would like to login.
Users that do not have an account on the computer are Not part of the Everyone Group.
If security on the LAN is
Not needed and users are Not established, then switching On the
Guest account provides semi-open configuration.
http://windows.microsoft.com/en-US/windows7/Turn-the-guest-account-on-or-off
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Point to the a Folder that meant to to be share. Right click and choose properties.
In the properties
Click on the Security tab shown in the pic bellow to the right) and check that the users and their permission (shown in the pic bellow center and left) are correctly configured. Then do the same to the Permission tab.
This screen shot is from Win 7, Vista's menus are similar.
http://www.ezlan.net/Win7/Permission-Security.jpg
In both the Security panel, and the Permission panel you have to highlight each User/Group and examine that the Permission Controls are checked correctly.
When everything is OK, Reboot the Network (Router, and computer).
* Note . The Groups and Users shown in the screen-shoot are just an example. Your list will look the way your system is configured.