I have just installed ntcoda-b1.exe and have had success (I think).

Windows XP version 5.1 (Build 2600.xpsp_sp2_gdr.050301-1519 : Service
Pack 2)
Cygwin: 1.5.18(0.132/4/2)

I do have a couple of comments to make about the process, I hope these
can be helpful.

I could not find anything that suggested what packages of Cygwin to
install.  So I installed the base package.

Ran the coda setup. Received notification that I was missing Perl. 
Re-installed Cygwin with Perl.
Ran the coda setup. Received notification that I was missing cygrunsrv.
 Re-installed Cygwin with cygrunsrv.
Ran the coda setup. Installed successfully.  Ran 'net start venus', and
noticed my N: display.
Ran vcodacon and received an error that I was missing the fltk
library.
Ran the coda un-install, received an error saying it was missing the
uninstall.log
Re-installed Cygwin with fltk library.
Ran the coda setup without having uninstalled the previous on, due to
the error (with fingers crossed) it re-installed.

If would be nice to have a list of the minimum components to install. 
The installer isn't checking for fltk as a dependency.

I followed the guides and everything seems to be working.

Is there a sample coda server/realm I can use to see or test if it is
really working properly?  Since my implementation would depend on a
successful WinXP client I thought it would be prudent to test it against
a working server before trying to set one up myself.