You are on the right way.
What is the output of:
C:\wamp\bin\php\php5.3.4\php.exe -f C:\wamp\www\dokuwiki-2010-11-07a\bin\grapher.php -h
It should output something like:
WS8 bin # php -f /var/www/dokuwiki/bin/grapher.php
digraph G {
"page-start" [shape=note, label="start\nStartpage", color=lightblue, fontname=Helvetica];
}