A couple of things right away
The code you have attached is measuring light, that's what photores do, it is a light dependent resistor..
What is the source of the PID library (Where did you get it, please provide a link)
what errors are you getting, please provide the errors as an image or written
if you want High and Low temperature and could also want humidity too, as this is common on weather stations, you might want to look at this DHT22 temperature and Humidity Sensor with Arduino Uno and Ethernet Card (ENC or WizNet) (Instant weather Station)
there is also the DS18B20 Arduino Playground - OneWire
and a PID library from here Arduino Playground - PIDLibrary
Armed with these libraries and the sample code you have you should be able to adapt the example to work with temperature.
If you try and cant get too far then please come back , post the code you have and we can try to help more
also in the sample code provided you had many instances where the comments continued on another line causing errors
the attached is with this corrected and it compiles without errors but still working as a light sensor control, not a temperature
pid_test.ino.zip 1.3 KB