actually this is written for a hackvision atm but changing it to work for the video game shield would be easy (i have both). The only thing is this requires the latest TVout as it uses TVouts version of millis() and the new bitmap function which is a very recent addition. All the other changes would be simple to get working on the version of TVout that nootropic has posted for the hackvision.
The simple tetris clone is a great bit of code it takes care of all the computation you are just left to code the input and output.