http://arduino.cc/playground/Learning/OneWire
"Each 1-Wire device contains a unique 64-bit 'rom' code, consisting of an 8-bit family code, a 48-bit serial number, and an 8-bit CRC. The CRC is used to verify the integrity of the data."
Each call to ds.search(addr) fills addr with one device address and returns 'true' or returns 'false'/0 if there are no more devices. You can reset the search and start over from the beginning by calling ds.reset_search().