Código PHP:
//Por ejemplo:
$conn=mysql_connect("localhost","xxxx","xxxx");
mysql_select_db("tu BD",$conn);
$sql="SELECT UsuarioID, User_P, Password_P
FROM `Usuarios`
WHERE 1 AND `User_P` = '$USER'
AND `Password_P` = '$PASS'";
$rs=mysql_query($sql,$conn);
if(mysql_affected_rows())
{
while($row=mysql_fetch_array($rs))
{
echo $row["User_P"];
}
}
else
echo"No se encontro";
Saludos