It's pretty easy to do, but it definitely isn't a perl question...

it depends on the sort of sound you want to play. if it's a stream of some sort then you will need to read up on the javascript interface offered by the plugin which is playing it. they're usually pretty simple.

if it's just a ping or beep or something then it's simpler. i haven't done it for a while, but i remember netscape used to have a built-in plugin for midi and wav files, and i expect something similar is still true. All you need is the embedding syntax - which is simple - and the right javascript call. document.embeds[0].doPlay() is likely, but i can't remember.

suggest you try devedge or (sorry) msdn.