So, following with my Tinkerlab project: I'm back to business as I finally got some components: an Arduino UNO, the ID-12 reader, some 125KHz RFID tags and the USB base for the ID-12, all from Sparkfun.
The first thing I did was just plugging the USB reader to my laptop and playing around with the tags to see if I had bought the right type, and fortunately for me, I did (I had surfed way too fast on the Sparkfun website, so I was kind of afraid that I had bought the wrong ones). Then I hooked it up to the arduino and wrote some code based on what Martijn The did with BARRAGAN’s code.