Geez that is really good. The BG definitely has that moody dark techno grunge-y feel going on to it, and seems to go perfectly with Lain (I'm assuming that's her..never watched the anime, though I intend to.) and her haunted look.
On a side note, not sure if html works here...could be xhtml which I heard that you have to do all the tags in lower case, but I haven't checked it out.
But back on track, you two did a great job. Now if only I were as good. :) Rock on, niXan and Kane!