Temperature sensor should use resistor?
You should give more information if you want us to help you properly. You're looking at the parts, we can't see them. You talk about a datasheet, then give us a link to it!  

If the temperature sensor has two wires it's probably an NTC thermistor (Negative Temperature Coefficient). That's a resistor whose resistance varies with temperature. You use the other resistor to make a resistor divider:  



Connect Vin to the Arduino's 5 V supply. Vout goes to one of the Arduino's analog inputs. As the resistance of the NTC varies Vout will vary as well. For a low NTC resistance the output voltage will move towards Vin, if the NTC's resistance increases the output voltage will decrease.

edit (after you specified the sensor)
Well, that was for an NTC sensor. The DS18B20 you seem to have is an IC which interfaces serially with the Arduino:

  

Connect VDD to the Arduino's +5 V supply, and the resistor between the 1-wire bus and +5 V (that's the VPU). These are the connections:  

  

Like Oli says it's a bit more complex to use than the NTC I mentioned, and the Arduino Playground page he mentions may help you to get started.