Ok I've added another cheat however I'm not sure if it's usable by anyone other than me as the code is assigned to a button on my joypad not the keyboard jump key. If I have time I'll sort it out.
Thief - Deadly Shadows v1.1
Created by Bleep!
Infinite Items :- Ctrl+1
Infinite Cash :- Ctrl+2
Quick Pick :- Ctrl+3
Levitate :- Ctrl+4 (Note 1)
Infinite HP (On) :- Ctrl+Pgup (Notes 2)
Infinite HP (Off) :- Ctrl+Pgdn
Note 1: The cheat was actually created for button 5 on my joypad, whether or not it'll work for your pad remains to be seen..
Note 2: The Infinite HP cheat will sometimes disable some portals.
Just quicksave then load the save to enable the portal.