You don't need any extra software to unzip zip files on Windows. Just double-click on the file icon and Windows shows the contents as if the zip file was an ordinary Windows folder (directory).
But if you installed Winzip, it probably hijacked that behaviour, to make you think you reallly really need to buy Winzip!
If you want to create a zip file, or uncompress other formats, try http://www.7-zip.org/ (which is free).