By the way -- why did you put the option "w" into "-xwzf"? Previous suggestions stated "-xvvzf" (though admittedly the repetition in "vv" is redundant: you can just as well use "-xvzf"); maybe you misread "vv" as "w"?
I copied "tar -xvvzf" from the examples on the manual page. Maybe the double v means, "be even more verbose"?
Richard