With *.tgz files you just need to install them (they are gzipped tar files containing the precompiled binaries).
In the directory containing the package to install, type:
and enter the root password, then
Code:
installpkg slackpkg*.tgz
or after typing su, you can as mcd suggests type:
Then choose 'current' (assuming you are in the same directory as the package you wish to install.) If it's the only package there, say 'Yes', if not, you'll need to go through whatever other packages are in the same directory and decide if you wish to install them as well.
(Look over this chapter of the updated 'Book' to learn more about Slack's package management:
http://slackbook.lizella.net/chapter18.html)