What about DOS? The deal with DOS is that one is loading a virtual floppy called A: into extended memory and then booting from this floppy. So you have to capture an image of a bootable DOS floppy first. Some more details can be found in the mknbi-dos directory.
I have booted DOS (both M$ and DR versions) diskless this way. A contributed mkfreedosnbi is also available for building tagged images for booting FreeDOS, but the procedure differs slightly from booting M$ or DR DOS. Note that extended memory is used so that rules out 086/088 computers but 286s are ok. See this document for more details.
If you were thinking of booting a Windows machine via the network, it seems (I'm not masochistic enough to do this) the problem is not the network booting but the mounting of a file system over NetBIOS (Windows does not do remote mounts of root filesystems over NetBIOS on TCP). So that rules out a Samba server. It appears to be possible over a Netware server, for which Linux or FreeBSD has workalikes. But then what do you do about the networking stack? This situation may change with with future Samba developments. But you will still have problems with pathnames and the usual Windows hassles. Do you really want to do this? In the Web page for Etherboot, there are links to Web pages, one explaining how this was done with a commercial TCP/IP boot ROM, another explaining how to do it using Etherboot and Netbios over IPX.