We have a SuperCheats.com exclusive game guide for Bioshock here:
http://www.supercheats.com/guides/bioshock/

There is a full walkthrough with screenshots and well as an overview of the game's weapons and enemies.

There is also a guide for all 122 Audio Diary Locations, Tonics list and weapons upgrade.

Where you installed Bioshock, search for the file 'defuser.ini' and open it up with a plain text editor, such as Notepad.

Now you'll see alist of keystrokes, such as F1 etc... You now need to enter what you would like those keys to refer to, so just enter as follows :

F1=fly

This will give you the fly cheat everytime you press F1. A full list of possible cheats and their effects are listed below. Just allocate whatever keys you want using the same method above.

Fly - Fly Mode
Ghost - No Clipping Mode
Givebioammo - Gives EVE
Givehealth - Get More Health
Igbigbucks - Get $500
Killpawns - Kill All Enemies on Level
Slomo - Slomo Mode
Suicide - Kill Self
Teleport - Teleport to Crosshair
Walk Remove - Fly and Ghost modes

Don't forget to make a backup up all files you edit in case you make a mistake.