What do you get applying FFT to Music?
Yes, you should be able to see the component of the piano note. But there are quite a few pitfalls on the way. I would suggest you experiment a little to get a 'feel' on how fft works first. Use GNU Octave or Matlab to do simple experiments, and then you can plug in your real data, and see if it works. For example, in Octave I can easily generate a sine wave of 440 Hz and do the FFT:

t = linspace(0, 2*pi, 44100);
s = sin(440.0 * t)              % This is the 440 Hz tone
f = abs(fft(s))                 % Take the fft (magnitude)
plot(f)
xlim([0,1000])                  % Show only the 1000 first bins


Then you can read your samples and do the same. At least, this way you
exclude insecurity about the fft function you're using. You could also
save the generated sine, and feed it to your four1 function, and check
if the result is correct.