To configure a Mac OS X user account so that .DS_Store files are not created when interacting with a remote file server using the Finder, follow the steps below:Note: This will affect the user’s interactions with SMB/CIFS, AFP, NFS, and WebDAV servers. Open Terminal. Execute this command: defaults write com.apple.desktopservices DSDontWriteNetworkStores true Either restart the computer or log out and back in to the user account.
via Mac OS X v10.4 and later: How to prevent .DS_Store file creation over network connections.