Submit data into mysql database using wordpress?

I’m having trouble figuring out a way to insert data into my own mysql database setup within wordpress. What am I doing wrong?

http://carlots.net/blog/cars-3/

<?php

global $wpdb;
$name = $_POST['name'];
$email = $_POST['email'];
$phone = $_POST['phone'];
$address = $_POST['address'];

$table_name = $wpdb->prefix . 'customers';
$wpdb->insert( $table_name,
array( 'name' => $name,
'email' => $email,
'phone' => $phone,
'address' => $address),
array('%s','%s','%s','%d',));
?>

<form type="post" action="cars-3/" >

<label for="name">Name:</label>
<input name="name" type="text" />
<br/>
<label for="email">Email:</label>
<input name="email" type="text" />
<br/>
<label for="phone">Phone:</label>
<input name="phone" type="text" />
<br/>
<label for="address">Address:</label>
<input name="address" type="text" />
<br/>
<input type="submit">
</form>
<br/><br/>
<div id="feedback"></div>
<br/><br/>