Actually from the PHPSlash site (http://www.phpslash.org/):

Contributed by Joe Stewart on Tuesday June 18 2002 @ 12:33PM
  [http://www.postnuke.com] - Greg Allan a.k.a. Adam_Baum, the lead core
developer and one of the four founding members of the PostNuke CMS
Development Project passed away from injuries sustained in a motorcycle
accident. The accident occurred June 16, 2002 near his home in Meaford,
Ontario in Canada.

This bodes ill for them ever getting the install process documented...