You have a database full of items you want to post on twitter. If you are not familliar with oauth or do not have a real use for it (you manage your accounts through scripting), basic auth is the way to go. Here is our quick and dirty poster:
This is just rough code, add the bells and whistles yourself.

The following table is assumed:

CREATE TABLE IF NOT EXISTS `items` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `item_number` varchar(5) character SET ascii NOT NULL DEFAULT '',
  `description` varchar(50) character SET ascii NOT NULL DEFAULT '',
  `price` varchar(4) character SET ascii NOT NULL DEFAULT '',
  `url` text character SET ascii NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=144845 ;

Your PHP db function:

 
function agent_db()
{
$dbuser        = "your db username";
$dbserver    = "your host";
$dbpass        = "your db password";
$dbname        = "your db name";
 
//CONNECTION STRING
$db_conn = mysql_connect($dbserver, $dbuser, $dbpass)
or die ("UNABLE TO CONNECT TO DATABASE");
mysql_select_db($dbname)
or die ("UNABLE TO SELECT DATABASE");
return $db_conn;
}

Your Tweet Function:

function tweet($message, $username, $password)
{
$url = 'http://twitter.com/statuses/update.json';
$fld = http_build_query(array('status' => $message));
$ch = curl_init();
 
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_USERPWD, $username.':'.$password);
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $fld);
 
$ret = curl_exec($ch);
 
return $ret;
}

Now let's loop on the items:

$sql = "SELECT * from items;"; // Limit 0,50 if you do not want to be marked by twitter - Go easy on mass posting
$result = mysql_query($sql,db());
while ($row = mysql_fetch_assoc){
$item_number = $row['item_number'];
$description = $row['description'];
$price = $row['price'];
$url = $row['url'];
 
$post = "$item_number $description $price $url"; // That can be anything ..just has to be 140 char .. which you should test before sending .. Add it ! <img src='http://www.michel-angelo.net/wp-includes/images/smilies/icon_smile.gif' alt=':)' class='wp-smiley' /> 
 
$tweet = tweet($username,$password,$post);
// you can test $tweet for error when the function is done returning the value, to see if the post was successfull or not;
echo "$tweet\n
";
 
}

Taaadaaa !
See Ma' no class!
You can also replace the tweet function by the following if you do not have the Curl library installed (Original Post from Fabien Potencier):

function tweet($message, $username, $password)
{
  $context = stream_context_create(array(
    'http' => array(
      'method'  => 'POST',
      'header'  => sprintf("Authorization: Basic %s\r\n", base64_encode($username.':'.$password)).
                   "Content-type: application/x-www-form-urlencoded\r\n",
      'content' => http_build_query(array('status' => $message)),
      'timeout' => 5,
    ),
  ));
  $ret = file_get_contents('http://twitter.com/statuses/update.xml', false, $context);
 
  return false !== $ret;
}