PaperlessPrinter making ANY PRINTABLE DOCUMENT into an eBook for use on PSP or DS. The software is like similar warez that print to PDF - but it prints to a customized aspect ratio of sequentially named JPGs.
The PSP will permit you to simply drop these JPGs on a stick but the DS is a little trickier. Once you have your images - it's just a matter of packaging up those JPGs with one of the many GBA slideshow softwares and Flashing to a writable cart.
It's free and you're bored - get to it.