Windoze has a unzip program built in (Windows XP and (i think) 2000), so WinZip is not nessacary. By the way, I got that message when trying to download Flyakitev3.0, using the Windows XP Unzip app, but that was when I had FlyakiteOSXv2.0, and used Internet Explorer. I downloaded Firefox, downloaded the file, and the Zip was fine.
HINT: Download Firefox (from here
) and the zip may become not corrupt.