Display your website name in the HTML title of your Joomla 1.5 page

Add one of the following blocks of code to the top of the file and save.

<?php
 
$mydoc =& JFactory::getDocument();
$mytitle = $mydoc->getTitle();

$conf =& JFactory::getConfig();
$sitename = $conf->getValue('config.sitename');

$mydoc->setTitle($sitename.' - '.$mytitle);
 
?>

Taken from here.