Windows Media Player (WMP) has these settings to "arrange my music" as well as updating information about the files.

I wonder what you decided to set these to? Can you share this WITHOUT checking the control panels? I found most to be unaware of these settings and later ask about why files went missing or changed.

Also, if you are using the WMP server feature, that server would be the other user. Here's a note about that -> http://windows.microsoft.com/en-US/windows-vista/Sharing-media-on-a-network-using-Windows-Media-Player KEEP reading it and there's a link to turn it on and off.
Bob