it largely depends on the type of field that your date field is
in general, if you want to set date = today, you can just do
"INSERT INTO dates VALUES(NOW())"
and use the mysql now() function.
if the date is a mysql timestamp, the format is YYYYMMDDHHMMSS
$date = date("YmdHis", getdate());
$sql = "INSERT INTO dates VALUE($date)";
if the date is a mysql datetime,
$date = date("Y-m-d H:i:s", getdate());
$sql = "INSERT INTO dates VALUE($date)";
note mysql tables have a 'feature' whereby the first timestamp field in a record will be updated every time the record is changed - even if that field is not changed. to get around this, have a lastupdated field (of type timestamp) that will be the one to change.
adam