CTRCheater can be used to patch the classic Tomb Raider games (Tomb Raider 1 to 5) in order to add a variety of cheats.
The following cheats can be applied:
Invincibility (All five games)
Infinite Ammo (TR 1-3)
One Shot Kills (All five games)
Multiply Gun Power (TR 1 only)
Simply unzip the file anywhere, run the program, select the .exe file of the Tomb Raider game you want to modify, choose your cheats, and then click 'Create Modified EXE'.
The program does not make modifications to the original .exe file. Instead, it'll create a new file with 'Cheat' appended to the end. You can then run the new .exe when you want to play with cheats, or the original when you want to play normally.
For Tomb Raider 1, you need the native windows version of the game. Doesn't exist, you say? That's what I thought! But you can find a patch to run a native windows version of TR1 here. It's great!