The sprites are compressed and divided into 8x8 tiles. At the beginning of an act, the 8x8 tiles are loaded into the video memory (VRAM). The obect who's using the sprite will point to the right VRAM address, and then "map" the 8x8 tiles into a sprite. To copy a sprite, you have to copy the compressed 8x8 tiles of the sprite graphics into the hacked ROM, then change the pointer so it can be loaded into VRAM, and then copy the "map" data for the sprite into the hacked ROM and then change the object's map-pointer to the right address :P
