I agree, you definitely need help.
1. How can I download firmware to Canon Power Shot SD 880 IS?? Step by step instructions Please!!
You cannot, the SD 880 is not yet supported. A firmware dump is not CHDK, its a plain copy of the software running on the camera - it is needed in the porting process.
2. My children put in my Canon A570 not correct batteries... after this camera died... is it possible to repair it in home conditions???
Depends - when you put a 9V block in the camera with the assitance of a sledge hammer, you most probably cant repair it. Otherwise, the camera shouldnt be damaged anyway. AA batterys are too small, everything else is too big.