simply don't set it, it will set itself automaticly, better get the TR64 v0.8.8 for best support. Also, don't forget to create the TILES folder in your main emu directory before you active the tiles dumper.
There is also the neme (Lemmy's) latest video plugin that can dump textures and vrml (3d). It ca n be used in 1964 and nemu64 but not in PJ64.