I too have found this problem. I returned a Targus keypad that didn't seem to be working AFTER I realized (reading the package after purchase and calling Targus) that the Targus calculator keypads were NOT Mac-supported.
I just purchased a Kensington KeyPad Calculator (model 33059) which is EXPRESSLY compatible with Mac and I cannot get it to work!! The first time I plugged the device in, the Keyboard Setup Assistant popped up which (1) I did not know what options to choose (the question prompted was to press the key immediately to the RIGHT of the LEFT-SIDE shift key on the new USB keypad and I DO NOT HAVE THAT...it's just a simple 19-key calculator pad!!) and (2) after not recognizing the keypad, the Setup Assistant gave me the option of choosing a 100+-key ANSI US default (again, NOT what the Kensington is--a simple calculator pad!!).
The Kensington has to mode of imput...keypad and calculator. I tried to use the calculator function on the Kensington while Apple's calculator was launched and, as Marc found, the input single seems to be the number and CLEAR!! (i.e., press '8' and you can see a flutter on the Apple calculator corresponding to '8' and 'C' for CLEAR resulting in NO input!).
Does anyone know how to set up or use this purported compatiable Kensington 33059 Keypad??
Thanks!
Scott