OOP query probleem

mensen,

ben begonnen met oop programmatie en er loopt iets kleins fout maar ik vind het niet.

ik wil simpel query uitvoeren

<?php
public function setUser($username, $name, $email, $password)
{
$this->username = $username;
$this->name = $name;
$this->email = $email;
$this->password = $password;
}

public function insertUser($table)
{
$sql = "INSERT INTO $table
(username, name, email, password)
VALUES
($this->username, $this->name, $this->email, $this->password)";

return $sql;
}
?>

nu stukje db class

<?php

public function query($sql)
{
$this->result = mysql_query($sql, $this->connection);
$this->numRows = mysql_num_rows($this->result);
}
?>

de index file

<?php
$db = new database();
$user = new user();

$user->setUser('anthony', 'twanie', 'twanie@', 'pasxx');
$db->query($user->insertUser('users'));
?>