Go to "My Madden", "Rosters", "Player Management", and finally to "NFL Greats". Release whoever desired, then go to "Free Agents" and put the desired player on a team. When you begin Superstar mode, go to play as a rookie and find your player. If you chose a great, he should be close to the top. This also works if you create a player. When you create a player and put him on a team, he is a rookie. He should also be there when you go to Superstar mode.