Take a look at this upgraded extension for WriteHTML with text alignment: http://fpdf.de/downloads/addons/41/.
Example (from the link):
<?php
define('FPDF_FONTPATH', 'font/');
require('WriteHTML.php');
$pdf=new PDF_HTML();
$pdf->Open();
$pdf->AddPage();
$pdf->SetFont('Arial');
$pdf->WriteHTML('You can<BR><P ALIGN="center">center a line</P>and add a horizontal rule <BR><HR>');
$pdf->Output();
?>