I was installing Magento, unzipped the files to a folder and accessed the URL but instead of getting the installation wizard I got 500 error. After much research I found that the issue was due to file permissions.

I had set the following permissions as per http://www.magentocommerce.com/knowledge-base/entry/magento-installation-cheat-sheet

777

• – file: magento/var/.htaccess
• – directory: magento/app/etc
• – directory: magento/var
• – all the directories under: magento/media

but I got 500 error. There were some other file permissions that I  had to set to make it work. Here the complete set of permissions required to make it work.

777

• magento/var/.htaccess
• magento/app/etc
• magento/var
• all the directories under magento/media

755

• magento/
• magento/install.php
• magento/index.php

644

• all other files

Detailed Magento installations instructions can be found at http://www.magentocommerce.com/wiki/1_-_installation_and_configuration/magento_installation_guide

Installation cheat sheet: http://www.magentocommerce.com/knowledge-base/entry/magento-installation-cheat-sheet