[Head416]

This is the Windows XP machine requiring credentials before it allows another device to access its shared printer. The XP machine will have no awareness of the credentials on the other machines.

That's also why I suggest including the "computername\" before the ID. "User" on the XP machine and "User" on the Ubuntu machine are two totally different accounts - like two guys named Bob.

Although, that just made me think of another possibility... sometimes if you create an account on two different machines with the same name and same password it will work. It's kind of a trick, but it might work. This is like having two guys named Bob Smith and people getting confused about which one they're talking about.