Last minute documentation-

Press CTRL+Y to configure multiplayer buttons (or joypad if present)
To select mutliplayer mode go onto either Normal or Ballistic Mode and when on the level select/menu screen enter the options menu

Player 1 controls are:

Direction keys- fly
CTRL- fire
Space bar- Free's the Zeon Shield
ALT+F4 - Quits game

oh and can you see why i abandoned this? yep... its buggy and i cant be bothered to clean it up