Create the /Library/StartupItems/Lighttpd directory, put both the Lighttpd (chmod +x) and the StartupParameters.plist (I don't really know what this does at all) files into the directory. (this is on jaguar, before the new launchd came out in tiger).

Then add the following line to /etc/hostconfig:

LIGHTTPD=-YES-

You can start, stop and restart lighttpd using /Library/StartupItems/Lighttpd (start|stop|restart) now, and it will startup when OS X boots.

-------- Lighttpd

#!/bin/sh
#
# /Library/StartupItems/Lighttpd/Lighttpd
#
# Script to startup lighttpd with OS X booting.
# OS X 10.3 Jaguar
# modified by kjell olsen
#
# adapted from the startup mysql
# (c) 2003 MySQL AB
# Written by Lenz Grimmer 
#

# Suppress the annoying "$1: unbound variable" error when no option
# was given
if [ -z $1 ] ; then
        echo "Usage: $0 [start|stop|restart] "
        exit 1
fi

# Source the common setup functions for startup scripts
test -r /etc/rc.common || exit 1
. /etc/rc.common

# change config and script to match your machine's lighttpd config and lighttpd
CONFIG="/etc/lighttpd/lighttpd.conf"
SCRIPT="/usr/local/sbin/lighttpd"

StartService () 
{
  if [ "${LIGHTTPD:=-NO-}" = "-YES-" ] ; then
    ConsoleMessage "Starting Lighttpd Server"
    $SCRIPT -f $CONFIG
  fi
}

StopService ()
{
  ConsoleMessage "Killing Lighttpd Server"
  kill `cat /var/run/lighttpd.pid` 
}

RestartService ()
{
        ConsoleMessage "Restarting Lighttpd server"
        /Library/StartupItems/Lighttpd/Lighttpd stop
        /Library/StartupItems/Lighttpd/Lighttpd start
}

if test -x $SCRIPT ; then
        RunService "$1"
else
        ConsoleMessage "Could not find lighttpd startup script!"
fi

Be sure to change $SCRIPT + $CONFIG to work with your own lighttpd.

-------- StartupParameters.plist

<?xml version="1.0" encoding="UTF-8"?>
DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Descriptionkey>
        Lighttpd 1.13</string>
        <key>OrderPreferencekey>
        None</string>
        <key>Provideskey>
        
                Lighttpd</string>
        array>
        Uses</key>
        <array>
                <string>Networkstring>
                Resolver</string>
        array>
        </dict>
plist>

Again, I'm not exactly sure what this does. I copied it from the MYSQL one and changed the description and provider, left "uses" alone.