Help Editing Tony Hawk's pro Skater 1

Does anyone know where the textures are for the levels and skin are located in the game. I already changed all the music and most of the movies, and the boards. The skins are not pvr files. I suspect they are located in files that end with *.psx or *.kat, but I have no idea how to edit or extract from these files, or what ever. Is there a page for editing dreamcast back up games?