Implement a new data type

[mohand oubelkacem makhoukhene]

Hello;
I whould like to implement a new data type next to char, number, varchar... A 
Money type.
So i'll have to change the source code, but i don't know which fonctions i need 
to change and which part to work on.
I need some help to implement this new data type.
Thank you and best regards
Mohand