John Landamore started an interesting thread on the Linux CIFS Client mailing list. He pointed out that W2K, W2K3, and W/XP can all mount subdirectories of a share, as in:

net use N: \\SERVER\SERVICE\SUBDIR1\SUBDIR1.1

Watching on the wire, it seems that the client is performing a traditional TREE_CONNECT_ANDX to the share itself (not the subdirectory). After that, the client performs all operations relative to the specified subdirectory. In other words deep mapping occurs on the client side.