http://www.webweaving.org/ical/
The recently released iCal can publish calendars; either to your .mac
account - or to any DAV enabled webserver. Apache 2.0 will work just
fine
out of the box; for apache 1.3 - from version 1.3.27 you are fine;
earlier versions need a patch (see below) as apache was somewhat too
strict in its Digest authentication parsing.