Page titles in Joomla 1.5 are not particularly configurable. I prefer to use an SEO extension, which gives me total control of my page titles and metatags, but I understand the reluctance to rely on a non-commercial extension. Will it be around for Joomla 1.6? Who knows?
The problem with Joomla 1.0.X page titles was that they insisted on putting the site name in the page title. Joomla 1.5 cured that disease, but some people would still like to have their site name in their page title consistently across the site. For that, the perfectly simple solution is the Title Manager extension for Joomla 1.5 (native).
Download, install and activate this plugin, and you will have your Joomla site name, or another text string of your choosing in all page titles. You can even configure whether or not the page title goes before or after the original page title, as well as the seperator character. Here’s a peek at the configuration screen: