Have a read of the above link re Vista File and Printer Sharing.
How to give Permissions are there, too.
1st thing to do is make sure that the Workgroup Name of ALL the computers is
In Vista Network and Sharing:
Network Discovery: ON (So it can see the other computers)
Network set to Private (Public is for hotspots, airports, etc)
File Sharing: ON
Public Folder Sharing: ON (Vista Public Folder is the same as XP Shared
Password Protected: OFF (unless you want to set up identical usernames and
passwords on ALL computers in your Network)