Samba uses SMB protocol (which Windows uses natively) so that works all right, no problem. You can copy a document to your friends computer over the lan if he's running XP and you're running Slackware, if you just have Samba installed and are granted access (like username/password if needed) to the shares.
As I read the first paragraph of the reply as quoted above, there is no confusion at all. You can read and write to a Windows share on your LAN using Samba provided you can successfully log in to the Windows computer. This has been true for quite a while.
The question of reliability only comes into play when a Linux system is trying to write directly to a partition formatted with the ntfs file system, usually on the same computer.
The difference is that when a Linux computer is writing to a Windows computer using samba, the Linux computer is not actually writing the data to the Windows partition. It is instead sending the information to the Windows computer, and Windows is writing the data.
When a Linux computer is writing data to a Windows partition on the same computer, the Windows OS is not running, so Linux has to write the data directly. This is where the trouble comes in. ntfs is a proprietary file system, and its specification is not publicly available. Microsoft can change it at any time. They have no obligation to provide the details of the ntfs specification to any third party (including the Open Source Community). As a result, any third party attempt to write to an ntfs volume will be an exercise of observation and guesswork at best. Even if the Open Source community learns to write successfully to an ntfs volume today, there is no guarantee it will work in future versions.