main () {
    #include <stdio.h>
    #include <unistd.h>
    setuid( 0 );
    //printf( "C Program\n" );
    system ( "/var/www/lock/lock.sh" );
}

So rdieter told me I needed DBUS_SESSION_BUS_ADDRESS.
I believe this works, as it outputs:
<unix:abstract=/tmp/dbus-L10p2odN6R,guid=b399a25e904a2ecd9fb969210001258f>


#!/bin/bash
# We must set the DISPLAY variable so dbus is happy.
export DISPLAY=:0.0

# We must find the DBUS_SESSION_BUS_ADDRESS so dbus is happy.
for pid in $(pgrep -u $USER)
do
     declare DBUS_SESSION_BUS_ADDRESS=$(cat /proc/${pid}/environ | \
             tr '\0' '\n' | grep "DBUS_SESSION_BUS_ADDRESS=")

# I looked for the first DBUS_SESSION_BUS_ADDRESS found.
     [ -z "${DBUS_SESSION_BUS_ADDRESS}" ] || break

done

# Strip off the DBUS_SESSION_BUS_ADDRESS= string at the beginning.
DBUS_SESSION_BUS_ADDRESS="${DBUS_SESSION_BUS_ADDRESS:25}"

# I echo it for debugging purposes...you probably don't want to echo it.
echo "Set bus address to<${DBUS_SESSION_BUS_ADDRESS}>"



lock.sh:
#/usr/kde/3.5/bin/dcop --user emmelin kdesktop KScreensaverIface lock
XAUTHORITY="/home/emmelin/.Xauthority" DISPLAY=":0" /usr/bin/qdbus org.kde.screensaver /ScreenSaver Lock
XAUTHORITY="/home/emmelin/.Xauthority" DISPLAY=":0" /usr/bin/xset dpms force off