The Problem is with your code formatting,
inorder to use strtotime()
You should replace '06/Oct/2011:19:00:02'
with 06/10/2011 19:00:02
and date('d/M/Y:H:i:s', $date);
with date('d/M/Y H:i:s', $date);
. Note the spaces in between.
So the final code looks like this
$s = '06/10/2011 19:00:02';
$date = strtotime($s);
echo date('d/M/Y H:i:s', $date);