You need to open the index.template.php and you'll see the part for the forum name in the header tables. Remove the php function for the name then find the image used in the background of that, it's one large image. Open either it or the psd file (get it from the theme's page at smf's themes site) and do what you want to it then save it. In the psd file, the slices should still be there, you just have to go to View>Show>Slices if you can't see them and then they should show up.
The real hell is your life gone wrong.