I've never transited through the States, but if you're travelling on the VWP then you put the address of the hotel or house where you are staying on your first night, and I think this still applies if you are in transit. You should be given help and advice either at your departing airport or onboard the flight on filling in the I-94W.
Depending on when you are travelling, you maybe able to use their new electronic travel authorisation system, ESTA - more information is available at
U.S. Customs and Border Protection - Travel