If you install php and mysql for the sole reason of running Mediawiki, and are inexperienced :-) and forget to uncomment ;extension=mysql.so, you get a blank page in your browser after running the script in config/index.php. Here is a patch to make it painfully clear what is going wrong in this situation. It checks for mysql prior to asking you to fill out that form.
-- Joshua Swink yathster@yahoo.com