There's no need to take care of the delimiter, all you need to care is the arrangement of the year,month,day only
You can insert date as a string in either 'YYYY-MM-DD' or 'YY-MM-DD' format. For example, '98-12-31', '98.12.31', '98/12/31', and '98@12@31' are equivalent.
Similarly, '2010-12-31', '2010.12.31', '2010/12/31', and '2010@12@31' are equivalent.
Refer this for more,
dev.mysql.com/doc/refman/5.1/en/datetime.html
So, I would suggest you ask the date either in preformatted format (YYYY-MM-DD)
or
create three input fields for YYYY, MM and DD separately.
Then at server side you combine them.
If you still want to go with your existing code. then use this,
PHP Code:
$date_php = '01/18/2011'; //assuming MM/DD/YYYY
$date_array = explode('/', $date_php);
$date_mysql = $date_array[2].'/'.$date_array[0].'/'.$date_array[1];