I'm going to japan in may and I would like to see MM the 17th on tokyo. Can someone help me and tell me how to buy tickets ?
First, see the shopping guide in the sticky section of this forum.
Then, Universus @ H!O wrote a great guide,
here. It's a bit dated but probably still valid.
Last, there are 'visiting Japan' threads on most H!P oriented forums. Try asking there.