CANBUS and OBD2 , Getting Car Sensor Values

Hi,

I want to make a project with arduino mega 2560. In the project, I connected gprs module, gps module. Successfully i can send my position data to my host-website. I will put this device to a car, it will connect with Car communication protocol and take some sensor values. These sensor values which comes from Car (CANBUS data) will be send over gprs module.
Problem:
I searched a lot, i found that, ODB2 sockets can communicate with arduino and send data. I dont know if these are can be used to connect with arduino (maybe some other versions are fits to arduino.). Which one should i buy? I prefer wired connectors.

Also i found Canbus shield can do that. But i am not sure, do i need both odb2 connector and canbus shield to sniff the car sensor value?

I simply found this sketch for Arduino Canbus Connection.

I made a circuit for one port canbus circuit.

here is the connection sketch for car and library
http://www.seeedstudio.com/wiki/CAN-BUS_Shield

Should i do this connection?

I have to do this project but our car is not available now, so if you know any computer program which acts like car and send random Canbus Sensor values, i will be happy.

At least, i would like to get a motor temperature value from Car canbus (or an emulator maybe from computer). I want to use my canbus circuit, any help or tricks will be beter. For example, i assume mcp2551 - 2515 is enough to get values from car. Should i connect my arduino power supply to car 12V and GND? I usually connect arduino to my pc and monitoring Serial.println() outputs from serial monitor. The 12V car voltage damages my computer?

Any help will make me happy,
Thanks you very much.