Edit the "WillowGame.ini" file in the directory:
"\..\Borderlands\WillowGame\Config".
Change the value of the following lines in that file to activate the cheats.

Effect 	                              Effect

Cannot drop below 1 health point        - Set "bDemiGodMode" to "true"
Weapon slot capacity                    - Set "WeaponReadyMax" to 2 to 4
Increase maximum inventory              - Set "InventorySlotMax_Misc" to a
higher number
Shoot own teammates                     - Set both entries of
"bIgnoreFriendlyFire" to "false"
NPCs can damage each other              - Set "bIgnoreNPCFriendlyFire" to
"false"
Bosses do not regain health after dying - Set "bBossesRegenHealthOnReset" to
"true"
Resurrect all players when someone dies - Set "bResurrectAllPlayersWhenOneDies
to "true"