...nwood...

1. I already had Cygwin installed. http://cygwin.com/
2. Grabbed these Cygwin ispell binaries: ftp://ftp.franken.de/pub/win32/develop/gnuwin32/cygwin/porters/Humblet_Pierre_A/V1.1/ispell-3.2.06-cygwin-1.3-bin.tar.gz (Here's the README.)
3. From the Cygwin shell:
   

    cd / #change to cygwin root dir impt!
   tar zxvf [path/to/tarball/]cygwin-1.3-bin.tar.gz
   

4. At the Windows desktop right-click My Computer and choose Properties, click the Advanced tab and then the Environment Variables button.

5. Highlight Path in the bottom pane and click Edit. Add the following directories to the end of your path:
   

   C:\cygwin\usr\local\bin;C:\cygwin\bin

   Now Windows can find both ispell.exe and cygwin1.dll.

6. Launch a new DOS shell (Start Menu -> Run -> cmd) and type:
   

   C:\Documents and Settings\luser>ispell -v
   @(#) International Ispell Version 3.2.06 08/01/01
   @(#) Copyright (c), 1983, by Pace Willisson
   @(#) International version Copyright (c) 1987, 1988, 1990-1995, 1999,
   @(#) 2001, by Geoff Kuenning, Claremont, CA.  All rights reserved.
   ...
   

   If you don't see that ispell output, there's probably something wrong with your PATH variable.

7. Launch a new Emacs. M-x ispell-buffer should start ispell.

Another option might be to compile the source here http://fmg-www.cs.ucla.edu/geoff/tars/ispell-3.3.02.tar.gz under Cygwin. I ran into missing programs and was too impatient to go through that.