I didn't realise it was possible on diesel (but I don't know a lot about diesel's).
The source code you linked to is indeed the right source code (here's a cleaner link
http://opengauge.googlecode.com/svn/...obduino32K.pde), what you need next is the arduino IDE - you can download it free from the arduino website, right here:
Arduino - Software
The code is easily loaded onto the arduino board via USB - you plug your USB arduino board into your PC, upload the code to it using the arduino software's upload button.
Once done, safely remove the arduino from your PC, and then set the OBDuino up with the other pieces - connect LCD display, ISO driver chip (MC33290 - where are you getting yours from?! - link please!), and resistors.
You might want to find an OBD plug for a cleaner install (i.e. to connect the OBDuino to the OBDII port in your car).
Note: I said in the above to put the code on the arduino board before putting your components in, the reason for that is so that your board is ready to go.
After you upload the code, then connect the display and other pieces.
Then, plug it back into USB so you can see the display works and the buttons work before proceeding further with getting it into the car.