While I’m definitely not a hardcore Nix user (unless you count the Darwin kernel in Mac OS X) I’ve always heard that Slackware is for the technical types.
Debian is supposed to be much easier for beginners to upgrade and manage than Slackware. If that’s the route you wish to go — check out this website and do a search for “Debian tutorials.”
The following link is a great place to start. I am currently going through the steps for installing Debian GNU. Follow page by page until completion.