Installing of Joomla! 1.5 is pretty easy. We assume you have set-up your Web site, and it is accessible with your browser.
Download Joomla! 1.5, unzip it and upload/copy the files into the directory you Web site points to, fire up your browser and enter your Web site address and the installation will start.
For full details on the installation processes check out the Installation Manual on the Joomla! Help Site where you will also find download instructions for a PDF version too.