Insert current date in datetime format mySQL

Try this instead

$date = date('Y-m-d H:i:s');

If you're looking to store the current time just use MYSQL's functions.

mysql_query("INSERT INTO `table` (`dateposted`) VALUES (now())");

If you need to use PHP to do it, the format it Y-m-d H:i:s so try

$date = date('Y-m-d H:i:s');
mysql_query("INSERT INTO `table` (`dateposted`) VALUES ('$date')");