When we first used the DS18B20, I tried Peter's code example. However, it failed with more than 2 devices on the line. I plugged in the Dallas app note code, and everything worked.

Also, not to sound like an echo, but please read the data sheets and app notes. All of them. Carefully. Especially if you will be wiring the sensors over a long distance wire. The software (and hardware) become much more complicated if you want to exceed 10 m of wire.