I had problems with check sums when untaring on a Solaris box. When you are saying unzip do you mean that the file ends in tar.gz or .tgz? If you gunzip the file and then tar -xvf the file and get the check sum then you might need to get gtar.
Try http://www.ibiblio.org/pub/ select your OS then down load the binaries (you won’t have to make the files just copy the binary gtar file to the directory you want such as /bin or /usr/local/bin.)