GoblinX 2.7 was released July 10th 2008. It is a Slackware-based desktop distribution that includes several window managers. Amongst them, Fluxbox and WindowMaker should be usable even with computers built in 1990s. GoblinX uses slapt-get for package management.
Absolute Linux 12.1.02 is another Slackware-based distribution that can be used for lightweight installations. But, please use a non-root account for day-to-day computing unless you prefer danger to security and completely trust in yourself :-)