Regarding the tools and materials you can refer to Union Jack instructable - only additions here are old keyboard keys, around 300 of them actually (for surface of two "windows" 55x16 cm each) and 4 mm transparent Plexiglas which closed the windows.
For this table I had to take apart top of the pallet and nail the boards again, tightly one to each other. After few series of sanding and later on painting, I've closed these "windows" with 4 mm plywood from the bottom. Then I spread some universal (thick) glue and started with laying the keys, one by one. For this first iteration I had to cut pins (where key is connected to the board) from the bottom of each key in order to have more gluing surface on the key and to maintain the targeted depth. For the next version I would need to find some softer material, instead of plywood, so I can just push in the whole key (with pin) by hand. This would save a lot of time when doing this.
So, here it is, hope you like it and as always, geek on.