I use VectorLinux and love it. It has several window managers and I heard that it runs KDe even faster then Slackware (which it is based on). It's also very newbie friendly. The system I run it on is below. The biggest thing that will intimidate you is that it doesn't boot into the gui by default. When you load Vector you will login and then enter the command startx.
Right now I'm downloading slackware 10.0 but all the mirrors I've found say that the only way to get it is with bittorrent which can be slow.
Also try DamnSmallLinux. It's a Live Distro based on knoppix but is small enough to run on a 486 /w 16MB RAM. They also have instruction on installation on their website..