Justin,
This is more advanced stuff, with quite a few things to consider.
The html tag to add background sound is "bgsound". You specify a sound file and whether to loop continuously as parameters. Non-microsoft browsers prefer the "embed" tag.
That is the easy bit.
Sound files are subject to copyright. If the sound isn't composed and performed by you or someone willing to give you the rights, you need to arrange and pay for a licence to put it on a website.
Sound files are big. Good quality music will slow down your slideshow, especially with slower connections.
Some people prefer to view in silence, making you think about how to provide a silent option.
Finally, there are technical aspects concerning sound. Different browsers will perform in different ways, so even a well-written webpage may not function as you intended. <bgsound> only worked in one of the three browsers where I tried it. There is also the issue of streaming, i.e. allowing sound to begin before the whole file has downloaded. As this depends on how the webserver is configured, you have an extra layer of settings and testing to worry about.
My suggestion would be to leave sounds until the last stage of building your site, otherwise it may hold everything else up.
Nigel.
