It's using an older version of Slackware. I've had success running this on a Compaq Contura 486/33mhz laptop with 8 MB of RAM, and a 270MB hard drive. The trick on the 4MB system is to initialize the swap partition, and make it available during the installation process. The HOWTO describes how to do that.
I actually had an NE2000 PCMCIA card running fine on that laptop-- too- It served me well, in fact-- I could use that machine to ssh
into any of my other boxen. On top of that, I got Vim installed on it with syntax highlighting, so I could write little code snippets, and take fairly quick notes. All of this, and I still had about 110 MB of space left on the disc.