MySQL's Password function is a one way function, much like md5. There is no way to retreving the value of that field. What you can do though, is check and see if one matches, by comparing it to another one that has gone through the function too.
Ex:
// To check the password, lets run a query.
// pretend there is code before this, that has an input of the field password.
$sql_query = "SELECT * FROM users WHERE username = '$username' && password = PASSWORD('$password')";
$result = mysql_query($sql_query);
if (mysql_num_rows($result) == 0) {
echo "Wrong Password for $username";
}
else {
echo "Hi, $username";
}