I downloaded Audacity about a month ago, but wasn't able to do much with it because of my lack of experience in audio. However, I was recently looking through some samples, seeking a good pipe organ, and didn't see exactly what I wanted, but found some things close to what I wanted.

What happened next was a break through for me. I accidentally opened the sample (one note) in audacity, and was able to view the wave form for that one note. Using the "generate tone" command to generate a second or so of square waves, I then was able to use the "envelope" tool to make a wave form that was a compromise between several of the samples I had found.

With that success, I've turned to making samples like those you might find on the NES or other pre-32bit era consoles. First, I find a .wav sample I like (of a violin, for instance) and examine the wave form. Then, I generate either a square wave or a "triangle" wave, and then use the envelope editing tool to reproduce that wave form.

I've had a lot of success with this technique, and as soon as I get some time I'll post some images. In the meantime, try downloading Audacity and examining various instrument samples that can be downloaded for free.