not really free but if I remember correctly you can continue to use it, haven't used it in ages so don't count me on that ..but it does look like you might have a trial version
you can try
http://www.7-zip.org/ ..Although not as good as winzip
I now use
http://www.win-rar.com/website/index.php?id=43&L=0 it is a much better as you can unrar just about any file including winzip files