I have written a small program displaying sounds and images on the screen when pushing any button. I always start it when one of my little kids crawls onto my lap and start
You'll need a keyboard hook. Unfortunately, this has to be done with P/Invoke; it can't be done with managed code.
Check out Baby Smash! by Scott Hanselman. It's hosted on code plex at http://www.codeplex.com/babysmash Github at https://github.com/shanselman/babysmash
Alternatively, check out ShapeShow on CodeProject, which is similar.