To access the Debug Mode and all the cheats, open the nwn.ini file located in your Neverwinter Nights folder, and add the following line underneath the Game Options:

Debug Mode=1

First, you will need to hit the tilde (Shift + ~) key and type in "DebugMode 1" (case sensitive). Then hit the (Shift + ~) key again and press [TAB]. This should show you a list of the different functions available. Hit [TAB] again to scroll down the list.
NOTE: Codes are case sensitive.

Code - Result:
dm_god - God Mode
GetLevel X - Adds X # of Levels to Your Char
dm_givegold X - Give Gold Amount X
SetCON X - Set Constitution to X
SetWIS X - Set Wisdom to X
SetINT X - Set Intelligence to X
SetSTR X - Set Strength to X
SetCHA X - Set Charisma to X
SetDEX X - Set Dexterity to X
GiveXP # - Attain XP
dm_mylittlepony - Mini Horse


Note: On some of the cheats, it will simply give you a message saying "success" after you type the code and press [ENTER]. Other ones, such as the SetCHA will say "Entered Target Mode". You must click on your character to enable the changes on your character.