(Untested)
$lines = preg_split("[\r\n]+", $_POST['text']);
$data = array();
foreach($lines as $line)
{
list($key, $value) = explode(':', $line);
$data[trim($key)] = trim($value);
}
At this point $data should be an associative array which you can reference to insert/update your database, or whatever else you want to do with it.