Save these two images as a 16 bit bitmap and use a firmware editor to compile them.
I also created this background because the default background got in the way of the text. Save it as both a jpeg and png, naming them both "wallp", and put them in system>res>a
This screenshot isn't very clear, but it gives you the general idea.
These are boot screens that I whipped up for this theme:http://www.4shared.com/file/Fq0EwwwJ/The_Legend_of_Zelda_-_ALTTP__L.html?cau2=403tNull
I don't take any credit for the theme or the original images used.