toofatkat - Milk does provide vitamins A, D, E, K, B1, B2, B6 and B12. Most of these you can get from other sources such as yoghurt (and the sun - vitamin D!) or in nuts and cereals. You don't need milk to get these vitamins. I am a bit of an anti-milk veteran though. Although I'm not vegan I still eat some dairy products such as eggs.
Also, its not recommended that you use meal replacement diets for longer than 3 weeks, so if you don't plan on getting your vits from anywhere else doing it for 3 weeks isn't going to hurt anyway.
Did you know we are the only animals that drink ANOTHER animals milk? Bit gross if you ask me lol