I have wrote about txz compression before. It is like tgz compression file. The easiest way to install software in slackware. And they have the same way to build txz compare to tgz.
For example I compile some software with these steps:
#./configure
#make
#make install DESTDIR=/tmp/mysofware
then this is how to build txz
#cd /tmp/mysoftware
#makepkg usr/mysoftware.txz

See the different when using makepkg. In Slackware 12.2 it will be like this:
#cd /tmp/mysoftware
#makepkg mysofware.txz

If slackware 13 use the same method with slackware 12.2, it will result an error