As the readme says and the "customized for you" shows, you need to name the images according to the pattern.

#categories li a.catBg9 {
background-image: url(../buttons/english/contactscrews.jpg);
will not work; you need to name it
background-image: url(../buttons/english/catbg9.gif);

If you want to use jpeg instead of gif files, you need to make a few edits to a PHP file as described in the readme (for the current v2.7.3).