While playing, press 'P' to pause the game and type "NCC-1701". Then press 'N'? The screen should flash. Press 'P' again to unpause and from there on, both players should have infinite lives.
After defeating a Goosecopter, fire continously at one of the tokens. After 32 hits, it will turn into a star, which when collected will yield mega-powerful six-way fire. Just be careful not to hit the token again before collecting it, or it will revert back to the one of the ordinary power-up tokens.