Cygwin/XFree86 can be used logon to a remote session using XDMCP (X Display Mangager Control Protocol).
Start Cygwin/XFree86 with a command similar to the following to logon to a remote session using XDMCP:
XWin.exe -screen screen_number widthxheightxdepth -query remote_host_ip_address -from local_host_ip_address
XDMCP is a complex system; further discussion of XDMCP is beyond the scope of this document.