i havnt messed around with graphics, so i'm not the right person to ask..
so i would suggest to either just try and change stuff and see where it leads or wait until one of the guys that have more experience with graphics comes around
it's just the default image that has been changed into the Z
if you roam around in the graphics folder of the skin, you'll find it
or you can take a look in this file,
generic/titlebar.xml
the links in the menu is in the file
menus/game.xml