Upscales the size of the interface making it larger for Higher Resolutions like 1440p in a "classic" style with elements of the marble and the f10 transparent styles kunark and velious had.
"HD" version upscales the individual .tga files with upscaled images of the original dragitems, gemicons, etc. From 256x256 -> 512x512 / 1024x1024 and makes them more visible less pixelated at a larger size.