I finally had a chance to install Cygwin and recompile Neptune's sample code for toggling the LEDs and backlight to run under Windows. Should make it easy to turn on the mail light from your mail notification program, etc. The Windows version has been sent to IA1Hacking.com and should show up at this URL within a few days:
http://www.ia1hacking.com/ia1_showfiles.php?category=windows
Original thread with technical info:
http://www.linux-hacker.net/cgi-bin/UltraBoard/UltraBoard.pl?Action=ShowPost&Board=MSNCompanion&Post=425
Incidentally, if you're just trying to get your screen backlight to turn off in screensaver mode under Windows, see this thread for a better solution:
http://www.linux-hacker.net/cgi-bin/UltraBoard/UltraBoard.pl?Action=ShowPost&Board=MSNCompanion&Post=581
Thanks to Neptune for providing the original Linux source for ia1led.