Slackware Linux is one of the oldest Linux distributions remaining. Over the years, it has stayed true to its roots and form.
Here's what the author, Patrick Volkerding has to say about it.
http://www.slackware.com/info/
The Slackware Philosophy
Since its first release in April of 1993, the Slackware Linux Project has aimed at producing the most "UNIX-like" Linux distribution out there. Slackware complies with the published Linux standards, such as the Linux File System Standard. We have always considered simplicity and stability paramount, and as a result Slackware has become one of the most popular, stable, and friendly distributions available.
What's this about "friendly"? You heard that Slackware was too damned hard, didn't you? If you are expecting cute graphical wizards and penguins automating every configuration step for you, that may be true. However, in essense, Slackware is one of the simplest distributions there is if you are proficient with a Linux system. If you aren't, a little perseverance with Slackware and you will be.
The reason it is easy for an experienced user is, first of all the init scripts and configuration files are easy to follow. They are generally well commented and it's easy to make changes using an ordinary text editor.
Not only that, you are getting the full, complete, standard releases of software in this distribution, installed in a sane manner. The way the developers intended. Therefore, when you go to install additional software not provided by the distribution vendor, you don't run into as many snags.
The packaging system in Slackware is quick, dirty and simple too. Slackware packages (.tgz files) are basically just tar.gz archives, that have install scripts that the packaging utilities execute. No dependency checking, which can be good or bad, depending on how you look at it. To me it's good, because I don't get annoyed by packages that won't install because of some brain dead mechanism that checks for things in specific places. The catch is, you need to be a bit careful installing system software.
Slackware also provides an excellent environment for building your own software from sources.
I could go on at length about why you should give Slackware an honest try but I'll let you follow this guide and see for yourself. We are going to be installing Slackware 9.1, which is the latest release at the time of writing.
Note: Slackware is now at version 10.2 and the installation routine has not changed appreciably, so this installation guide is still applicable.
Starting the Installation