it's not the dock background that is short...he is using one of TheAppleTree's theme (i think its YourTheme) and he is using the wrong icon...I'm pretty sure there are two icon for each of the applications and the wider ones end in _XXX or something. You need to SSH and change the iLauncher icon to the longer one. Like the simplicity, but this theme is meant to show if the background and your's is plain.