Projects like these always impress me, since they are a sign of a truly dedicated and talented developer. It takes quite a bit of both technical insight and dedication to pull of even a simple emulator - and having to make it run nicely in a browser doesn't improve your odds.

The output is a canvas element so it only runs on canvas-enabled browsers, and even then support is limited. At the time of this writing, Firefox 3.1 or Safari 4 beta should be your best bet.

Audio output is done with the help of .ogg files and the new HTML5 audio element, it didn't work too well for me, though - it only slowed down the emulation drastically but still no sound. YMMV.

Read Bruce's blog post for more details, including links to implementations on other platforms.