v. elementary problem installing Lexmark z600 printer driver on Lenny

[Lisi <lisi.reisz@gmail.com>]

I downloaded the tarball from Lexmark and have been following these 
instructions:

$ mkdir lexmark
$ mv CJLZ600LE-CUPS-1.0-1.TAR.gz lexmark # move the package to a folder. 
optional, but recommended. 
$ tar -xvzf CJLZ600LE-CUPS-1.0-1.TAR.gz # extract the driver.
$ tail -n +143 z600cups-1.0-1.gz.sh > install.tar.gz # the sh script is broken 
for newer systems. use `tail` to extract the binary portion of the script.
$ tar -xvzf install.tar.gz # extract the contents produced by tail
$ alien -t z600cups-1.0-1.i386.rpm # convert unusable rpm packages to tgz.
$ alien -t z600llpddk-2.0-1.i386.rpm # convert unusable rpm packages to tgz.
$ sudo tar xvzf  z600llpddk-2.0.tgz -C / # extract the tgz's to / putting the 
files in their right place
$ sudo tar xvzf z600cups-1.0.tgz -C / # extract the tgz's to / putting the 
files in their right place
$ sudo ldconfig # DO NOT SKIP THIS STEP or your printer backend won't find 
required libraries
$ cd /usr/share/cups/model
$ sudo gunzip Lexmark-Z600-lxz600cj-cups.ppd.gz # unzip the ppd, which should 
_not_ be gzipped

But I came unstuck at:
$ tar -xvzf install.tar.gz # extract the contents produced by tail
which produced the following error: (the gap between the command and the error 
message was put there by Bash)

dorothy@Lenny:~/Downloads/z600$ tar -xvzf install.tar.gz

gzip: stdin: not in gzip format
tar: Child returned status 1
tar: Error exit delayed from previous errors
dorothy@Lenny:~/Downloads/z600$

I am now stuck.  I realise that this is elementary and have spent a lot of 
time trying to solve it myself (Google etc.), but I need help!

Lisi