On the copyright screen, hold the Select button. On the title screen, instead of "Nerawareta Machi 1990" it will say "Amerikahen 1994". Now choose Start and the man will list the people involved with the game.
Sound Test
In the password screen ("Continue" in the main menu), enter 00999. Now, change the first two digits (00) to anything between 00 and 10 and press A to play any of the game's 11 songs. For example: to play the 5th song, enter 04999 and press A.