Hi Peter

It's a USB footswitch. Here's the link.
http://www.bilila.com/pagescore_turner

I might add that I am also using software called Pivot Pro which causes everything on the screen to rotate in this case 90 degrees to the right so all files and programs etc are easy to read and you don't get a stiff neck.haha

The Pivot Pro runs $39.95 but I was lucky and bought an unopened one on ebay for $9.
http://www.portrait.com/us/products/pp_overview.html

So I get to use all of the regular computer features of the laptop and the above 2 items are the only expense I have in this project which is minimal when considering the alternatives. All pdf programs are free.