YOURWORKGROUP\username
So, if your username is jdoe and the workgroup is HOME, try HOME\jdoe
* In order to confirm the workgroup name sent to samba server, check the logs (most likely located in /var/log/samba/). If the logs don't have enough information, increase the log level to 5 in the smb.conf file (/etc/samba/smb.conf) and restart samba service.
** If the domain name in the logs is not same as the workgroup name ("HOME" in example above), Windows is still sending the computer name as the domain name. Try mapping to the shared drive using the following command. Note, password is not supplied in the command. It is recommended that you save the password in Windows Credential Manager (see information below)
net use U: \\hda\Movies /USER:YOURWORKGROUP\username /PERSISTENT:YES
* Some windows clients for some reason may require the whole DNS path, so if your internal domain is, say, home.com, try: