Select the "Code Entry" option at the "Extras" menu, 
then enter one of the following codes:

Result                      Code
--------------------------------
Double damage             - 34743  
Unlimited stealth         - 53467  
Unlimited copper          - 23637  
Unlimited Chi             - 24463  
Unlimited health          - 94677  
One hit dishonor          - 54641  
Character concept gallery - 97831  
All treasure maps         - 37437