I'm just kind of getting sick of people feeling the need to remove parts/ecu software like these for warranty issues so I'll post this...its about the Magnuson-Moss Warranty Act of 1975:
http://www.impalaclub.com/naisso/magmoss.htm
(edit) I'll make it simpler: It is ILLEGAL for the dealer to "void your warranty" because of aftermarket parts. Unless of course the part is responsible for a problem and they PROVE that.