Use strptimeto analyze the resulting value, then dateto display it in the desired format:
echo date("M d,y", strptime("01/07/09", "d/m/y"));
If you are running Windows or using a version of PHP where it is strptimenot available (<PHP 5.1.0), use strtotime, but be careful that your date is in US English (that is, "01/07/09" means January 7, 2009 years, not July 1, 2009).
, jan, jan, strtolower:
echo strtolower(date("M d,y", strptime("01/07/09", "d/m/y"));