If your computer is running Windows XP, you should be able to extract the files without the need for a third party application like Winzip.
If you are not running XP, try doing a Google search for "zip freeware", and you will find links to a number of zip/unzip programs that are free. None of them are likely to be as user-friendly as Winzip, but they will get the job done.
All things considered, I concur with JimC's comment that Winzip is definitely worth the money.