Is that a D18B20 or a DS18B20?
There are loads of posts on the forum on getting the DS18B20 working with the Arduino.
Including example code.
Try searching the forum using google it works better than the forum search tool.
http://www.google.co.uk/search?hl=en&q=site%3Aarduino.cc+DS18B20&btnG=Search&meta=
Gordon