I have installed XAMMP 1.7.3 on my USB flash drive and it looks that it works fine.
Then I wanted to try a nice directory listing from the following link:
PHP Directory Listing Script (index.php + dlf folder)
and copied the index.php file + dlf folder to the htdocs folder.
Instead of a nice directory listing of the root, the text of the content of the index.php file was displayed in the browser.
This means that something must be changed in the settings (Apache?, PHP?) ?