This is a C++ class that will let you add 16-bit horizontally-scrolling text to your DS. Unlike the standard PALib text routines you can (in fact, must) work with 16-bit fonts and you can have the scroller running on top of another 16-bit image. You can even have multiple scrollers running at the same time.

http://ant.simianzombie.com/item/view.php?name=ScrollingTextDS