Zero-5

Cheat Codes:
At the Options screen, select Change Mission and highlight the high mission 
to be unlocked.  Hold Pause while entering code.  Sound confirms.
     Unlock Mission 1      0,5,0,5,0,5
     Unlock Missions 1-2   6,8,9,2,1,4
     Unlock Missions 1-3   1,2,2,1,6,9
     Unlock Missions 1-4   6,7,6,3,9,6
     Unlock Missions 1-5   4,9,3,1,7,5
     Unlock Missions 1-6   3,2,9,7,8,1
     Unlock Missions 1-7   7,4,8,6,2,7
     Unlock Missions 1-8   2,4,9,3,4,7
     Unlock Missions 1-9   (unknown)
     Unlock Missions 1-10  2,7,6,5,4,9
     Unlock Missions 1-11  1,0,7,8,4,0
     Unlock Missions 1-12  2,9,7,4,3,0
     Unlock Missions 1-13  9,2,1,7,5,3
     Unlock Missions 1-14  3,8,5,1,7,9
     Unlock Missions 1-15  9,0,1,9,3,4

NOTE: Entering a mission-unlock code will lock all missions above and beyond 
that one, even if you've previously unlocked them.