It seems the /etc/php5/apache2/php.ini file needs to be updated for this tutorial to work.
Uncomment:
extension=mysql.so
This worked to eliminate the error for me.
Found this in the following post:
http://www.idealog.us/2005/01/howto_fix_fatal.html
Hope this helps you.
Hopefully the tutorial will be updated to mention this potential failure point.