To make flying that much easier simultaneously
press [Left Shift] [Right Shift]  [Escape] 
during the aerial phases of the game. Or if 
you are finding combat tricky you can kill 
enemies with greater ease by pressing [Ctrl]
[Alt] [FIRE] all at the same time.

Codes:
32518581
33534548
88158744
23514145
14518783
41118181
44514182
56158745
76178741
85511634 (This one gets you past the infamous 
          Spanish Galleons)
38511276

You also get all 5 men with these codes.