I've got a sneaking suspicion that this is how the OP got his thumbs.db files too...
I didn't copy any file from XP machines, I was using vista before and there were no thumbs.db files there or I would have noticed. Those files appear on new folders
and have recent creation and last access times so they are created on the win7 PC. None of my folders are shared and I never accessed this machine from an XP computer. And all the software I'm using is the same software I was using on Vista and I've never
seen creating those files there so I really think it's Win7 creating them.
That's only true if the remote file system is NTFS. For all you know it could be FAT, HFS+, Ext3, ReiserFS, XFS......
Windows can know the filesystem of the samba share, if it's not NTFS it could save the stream data inside one of those pretty hidden files explorer loves so much.
A solution that only works sometimes isn't much of a solution.
Then why is the explorer team using them for the zone identifier? Knowing that explorer is already using them (zone identifier was added on XP SP2) makes this -omg streams shouldn't be used- argument pointless. You don't have support for compression or encryption
either on non-NTFS network drives yet that didn't make Microsoft stop using encrypted and compressed files.