Not all of the Win XP machines have the same password. I"m not sure I understand this part.
Finally, make sure you have defined the XP users (user name and password) on the Win7 machine – you don't need to log in with them, but these credentials will be used to grant access to the shared folder[/quote
Make sure "read and execute" authorizations granted to both the folder and the share include "everyone". Then make sure all the machines (including the Win7 one) belong to the same workgroup: even though workgroup is deprecated in Win7, it's still very much used in XP. [quote]Finally, make sure you have defined the XP users (user name and password) on the Win7 machine – you don't need to log in with them, but these credentials will be used to grant access to the shared folder
. I know it's a PITA, but unless you're in an all-Win7 network it won't work otherwise. Then, on the Win7 machine, don't let Windows manage the shared access, but turn on password access. That's in Network and Sharing center, homegroup and sharing options, advanced share settings. Check that the Win7 firewall allows file and printer sharing through. Last, on each XP machine, make sure network discovery is allowed: in Windows Explorer, Tools, Folder options, View tab, make sure the item "Automatically Search for Network Folders and Printers" is checked (in the advanced settings section).
Network discovery on an XP machine takes some time, especially with as many as 20 machines on the network. Allow all the machines to settle down for about an hour before attempting to access the share for the first time.