Putting Multimedia to Good Use.
Multimedia on the web is often seen as a bad idea: it breaks the flow of textual information, makes your bandwidth costs spiral out of control, and annoys visitors who aren't expecting it. Used properly, though, multimedia can enhance your website to no end, putting you light-years ahead of your competitors.
The Principle of Least Surprise.
The most important thing to remember with multimedia is this: never, ever include multimedia in a page unexpectedly. You think it'd be neat to put a video of yourself greeting your customers on your homepage? Maybe some background music for your product catalogue? For the love of God, don't. There are few worse things on the web than going to a website and having it try to throw unwanted multimedia at you.
The time to give your visitors multimedia content is when they have absolutely explicity asked for it. You should link to it with text like 'watch the video' or 'listen now', and leave it up to them what they want to do. Note that this also gives you a useful chance to ask the visitor which media player they'd prefer, instead of just trying to play things with one they might not have.
Audio on the Web.
Having been stung one too many times, there are a lot of users who only browse the web with their speakers turned off. For this reason, you need to give them something clearly useful to make it worth their while to turn them back on, and you need to warn them in advance that they will need to.
Once you've done that, what kind of content should you provide? Unless you're a radio station or you're providing an audio feed of something else that's happening live, streaming audio is generally a bad idea. You should also note that there is no royalty structure in place for web use of commercial music, so you can't really offer anything in that way either.
Instead, you should look at offering downloads of spoken-word mp3 files, divided into 'episodes' of about ten minutes or so in length. What you want to offer is entirely up to you: you could record some motivational speeches, or read the Bible, or whatever, if you think your visitors would appreciate it. The only rule is to keep it relevant and keep it useful – no-one wants to download and listen to plain old ads.
It's worth noting that web audio is undergoing a bit of a renaissance right now as a result of the iPod and so-called 'podcasting'. This is the practice of making short spoken audio segments available in a way that makes them easy to download to an iPod (or other portable music device) and listen to on-the-go. This is a practice that grows every day, and is well worth getting into.
Video on the Web.
What can you use video for on the web? Well, if you have a product you want to demonstrate, you could record it in action and offer that video for download. Generally, though, web video tends to be restricted to news and e-learning. In a commercial context, this means 'webinars' – videos that offer the web equivalent of a seminar presentation, made available for download.
When you make video for the web, though, you have some technical things to worry about. You should really make any video content available in three formats: Windows Media Player, RealPlayer, and QuickTime. Video authoring tools will save in all three formats, but it can often be complicated to write scripts that let users choose between these players and load them: you need to consider this when you design the website.
If push comes to shove, you need to be prepared for a segment of your audience to be just plain unable to view your video content, no matter how hard you try. For this reason, I would recommend that you make a text version of anything you say in a video available as a 'can't see this?' link, after you've offered some troubleshooting advice for common video problems. You might also consider taking screenshots of the video and making them available as static images, so that people who can't see the video aren't just forced to read a huge chunk of text.