They are not in tar but are gzipped tar files. The webbrowser or download agent is automatically g-unzipping the TGZ file into a TAR file. You should use a different web browser or use the command wget to download a TGZ file. In the commands below, I use 'wget' to download the mc-4.6.0-i486-4.tgz and then use the 'file' command to get a description of its format.
Code:
james@test-machine /home/james
$ mkdir temp

james@test-machine /home/james
$ cd temp

james@test-machine /home/james/temp
$ wget http://slackware.mirrors.pair.com/sl...6.0-i486-4.tgz
--09:53:20--  http://slackware.mirrors.pair.com/sl...6.0-i486-4.tgz
           => `mc-4.6.0-i486-4.tgz'
Connecting to 192.168.1.102:80... connected.
Proxy request sent, awaiting response... 200 OK
Length: 1,776,619 [application/x-tar]

100%[====================================>] 1,776,619      5.20M/s

09:53:20 (5.20 MB/s) - `mc-4.6.0-i486-4.tgz' saved [1776619/1776619]


james@test-machine /home/james/temp
$ file mc-4.6.0-i486-4.tgz
mc-4.6.0-i486-4.tgz: gzip compressed data, was "mc-4.6.0-i486-4.tar", from Unix,  max compression
Then to generate the MO file:
Code:
james@test-machine /home/james/temp
$ tgz2mo mc-4.6.0-i486-4.tgz
If you do not want to use wget or want to change browsers, then you can just g-zip up the TAR file into a TAR.GZ, then rename it to TGZ.
Code:
james@test-machine /home/james/temp
$ ls
mc-4.6.0-i486-4.tgz

james@test-machine /home/james/temp
$ gunzip mc-4.6.0-i486-4.tgz

james@test-machine /home/james/temp
$ ls
mc-4.6.0-i486-4.tar

james@test-machine /home/james/temp
$ gzip mc-4.6.0-i486-4.tar

james@test-machine /home/james/temp
$ ls
mc-4.6.0-i486-4.tar.gz

james@test-machine /home/james/temp
$ mv mc-4.6.0-i486-4.tar.gz mc-4.6.0-i486-4.tgz

james@test-machine /home/james/temp
$ tgz2mo mc-4.6.0-i486-4.tgz