To unlock a stadium, enter its code at the code 
entry screen:

       Astrodome -- FOR_RENT 
       Cleveland Browns Stadium -- DOGPOUND99 
       EA Sports stadium -- EA_STADIUM 
       Old Miami Dolphins stadium -- NOTAFISH 
       Old Oakland stadium -- STICKEM 
       Old Tampa Bay stadiums -- SOMBRERO 
       RFK Stadium -- THEHOGS 
       Tiburon (?Shark?) Sports Complex -- OURHOUSE