When they submit to form, connect to database, grab password, match it with the password they typed. If they match, INSERT into db, if not, don't insert.
$query = mysql_query("SELECT password FROM your_table");
$row = mysql_fetch_array($query);
$password_db = $row["password"];
if ($password_form == $password_db) {
// INSERT INTO DATABASE
} else {
echo "You did not type the right password";
}
That's the logic behind it, you'll have to modify it to suit your needs though. You could apply encryption to the password if you wanted to.
Cgraz