All-Stars Arena 1:
Select Exhibition mode and press X. At sub-menu, press R1, L1, R1, L1, R2, L2, R2, L2. Look under "Qtr. Length." You should see a new option, All-Stars. Turn this on to play in the All-Stars Arena.
All-Stars Arena 2:
Select Exhibition mode and press X. At sub-menu, press R1, R1, R2, R2, L1, L2, L1, L2.
Go to create player screen, then enter any of the names from the credits list in the back of the instruction manual. You can adjust the stats and when you score, the announcer will yell out the name.
If you want a better view of the cheerleaders during halftime, hold L1, L2, R1, and R2 buttons down at the same time. The game stats should disappear.
Thanks to Revolution readers Preston Lydia, Mikhail Sapozhnikov and Cyrus Alfshmidt!