After installing Mediawiki successfully, I got a blank page. Please note that I am using CentOS5/Apache 2.2/PHP 5.1.2
I went to /etc/php.ini and changed "display_errors = On". This will allow php errors to show up. After this, I got the following error message
Fatal error: Class 'DOMDocument' not found in /var/www/html/wiki/includes/Preprocessor_DOM.php
So, DOMDocument is not enabled by default in CentOS PHP. I installed it as follows
sudo yum install -y php-xml
This did the trick.