I’ve compiled Samba server (yes, the same server commonly found in Linux) under Windows using Cygwin.
Did not have time to test it yet (need to configure it), but I’ve found out that in fact some people are using samba for sharing on Windows (Google for “smbd.exe”). Perhaps the main benefit is the separate user account system which does not depend on Windows user accounts (you can create users just like in FTP server).
Will test the server later and update the blog with the results.

For those willing to compile samba themselves, the latest build (from samba.org) compiles fine under a complete Cygwin install (all packages), but the makefile might need to be tweaked to correct the output binary filenames (some filenames of samba binaries in the makefile will be without .exe extension) or samba might refuse to install (er. “make install”).