This project only uses parts from a keyboard (apart from the ball, couldn't find one in my keyboard) plus some adhesive material, depending on your preference.
Step 1: Materials
A ball to go down the bagatelle - I used the ball from a mouse because it was a convenient size, but it was a bit heavy. (just to be clear, I am on the keyboard side of the contest and only used the mouse because I had one close by)
Hot glue (or any other type of glue you think may work - blutack for a more temporary solution)
Glue gun (if you are using hot glue)
and a screwdriver for opening up the keyboard.
Step 2: Opening the Keyboard
Since the Image notes don't seem to be working, it seems that I'll have to put what I want to say below:
The first picture is of the keyboard that we're going to be wreck...uh I mean using. I'm joking (of course). If you only secure the keys with blutack then you will be able to put the keyboard back together afterwards - it might even work :)
The second picture is of the keyboard with the plastic back taken off.
The third picture is of all of the parts you should have. We will need the metal bit at the bottom, the bit with all of the keys on and the plastic backing. With the flexy plasticky bit that has circuits on I suggest you make something like this to use up as many of the parts of the keyboard as you can and be completely ecological.
Step 3: Pop Out the Keys
Pop out all of the keys that you'll need - If you are not sure how many you'll need then pop them out as you need them.
I found it easier to pop out the keys from behind but you can just do whatever you find easiest.
Step 4: Propping Up the Plate
You should end up with something that looks like the second picture below.
Step 5: Attach the Keys
The first thing that you should do while carrying out this step is to put the keys in the configuration that you think will be the most challenging/fun. Then you should glue (or blutack them) down in these places. I put in a semicircle halfway up that is quite hard to get into, so I made it worth 4 points.
Remember to put the number underneath each possible endpoint to signify their value.
Step 6: Add the Sides
Step 7: Fin
Just drop the ball down from the top and try and get the highest score you can.