I don't know where the graphics resources are stored off-hand ('..\static\imagelists' would be my first guess), and have not tried using any
extraction tools with DD (other than a dedicated program to get the
music).
There are some background tiles in the
fansite kit, but not the full background (with the artwork along the left and right edges).
A screenshot from a new game wouldn't have a lot of text to edit out, and if you took multiple screenshots from the different sections (quest log, conversation log, etc) at least some of the background covered in one screenshot should show up in another, reducing the amount you would need to replace.
You could also try emailing support@larian.com. The original resources might not be available somewhere that a specific graphic could be found with a reasonable amount of effort, but it can't hurt to ask.
