The improved Installer can be found under the Extensions Menu. With versions prior to Joomla! 1.5 you needed to select a specific Extension type when you wanted to install it and use the Installer associated with it, with Joomla! 1.5 you just select the Extension you want to upload, and click on install. The Installer will do all the hard work for you.
Additional Information
Newsflash
KORPUT will be soon providing Linux (Debian, Centos) Server Installation and Maintenance Consultancy service to companies which need key-turn automated server management at their IT infrastructure.