Also, it looks like you're using MediaWiki 1.3.x. 1.4 has been released, and now supports the MonoBook skin when using PHP 5.
-- Zigger
On 4/15/05, wrote:
... # PHP 5.0.3: the MonoBook skin will be disabled due to an incompatibility between the PHPTAL template library and PHP 5. The wiki should function normally, but with the older look and feel. ...