A great concept
And handy if peoples tuners are out of batteries, but even by your own admission, the strings are hard to click. What you should do to make it easier is to make the guitar visual closer up, also, go into the movieclips that are the strings, and make an alpha (invisible shape) which is wider behind each string so you dont have to click directly on the string to play it's note. That should solve all your button clicking problems, if you have any questions about this, feel free to ask.