At home I have XP Professional SP1, XP Professional SP3, Vista Business, 7 Ultimate & 8.1 Pro. I share data between them no problem without being asked for credentials when accessing shared folders. However, I have them set up so that I need to login with a user name and password for each one (I have several users per computer) and I keep the names and passwords in sync between them all. They are all in the same workgroup. If the username/passwords are different between the computers, then when you map a drive letter to the share you will need to provide a valid login set of credentials for the computer on which the share resides.