The 2007 is the 1st generation of Yaris. It was available in either a 4-door sedan or 3-door liftback in the US. The 2007 has the gauge cluster (speedometer, fuel gauge, etc) in the center of the dashboard. The 2007 looks like this:
http://media.treehugger.com/assets/i...is-2007-01.jpg
The 2012 is a newer-generation of Yaris. They look completely different. Also, the sedan is no longer available. They are only available in 3-door or 5-door liftbacks. The 2012 has the gauge cluster in front of the steering wheel. The 2012's look like this:
http://www.toyota.com/yaris/trims-prices.html