http://www.ignem.com/music/nes/zk-mathc.ittake a listen if you want, made it after my math exam today. nes-style owns.
for the curious nes comes with quite some limitations that are fun to work with. you have approx. 4 types of square waves that go 'beeeeeeeeep' to work with in two channels, one triangle wave that goes 'booooooooooo' in one channel, some 'krschshshcshhsch' (white noise) in one channel and a fifth where you can use imported sounds that may not reach above something like 32kb, meaning - low quality fun. some effects are allowed and basically the only i use are volume control, vibrato and portamento slide. enjoy!