please help (greyscale help)

so I need help on http://sta.sh/01yg1r2qzqba this....... I want to do some dithering but I think I need to start all over with the greyscale but I have no idea were to start??????? I use PS CS2 and gimp I would prefer to use it on gimp but I know in a lot of ways PS is easier. I also need some suggestions on dithering or possibly tutorials or brushes that I can use???????