The Playstation Portable has some annoying quirks when it comes to theme creation. I took on the problem and tried my best to convey it to the world what exactly you're supposed to do.
The most difficult thing to explain here was the formatting of the PNG images which took indexed color information (like the way GIFs are) but 8-bit transparency information (like the way 24-bit PNGs are). Small, unknown pieces of software allow you to combine the "best" (processor-efficient) of both worlds.