ok the DS is the first model it is the one that is bulky I am not sure of the screen size of any of them to be honest but I think they are similar. I do not have the original DS but I have seen them and I do think they are back-lit.
DS Lite is just what it says it is smaller and smiller lighter but basically the same as the DS in features as far as I know.
DSI has a camera and internet browser capabilities, the body style of the DS and the DSI are about the same the DS you are also able to play Gameboy advanced games the DSI no longer has that slot.
I have both the DS lite and a DSI if you have more questions let me know.
at 12:34 PM on Dec. 15, 2010