I’ve finally put together a slidecast on how to create a slidecast (very meta). It’s short (only 3 min), but it shows off the basics of how to use slideshare to make web multimedia using only a ppt file and an mp3.

It was interesting what I learned making this slideshow. The media form is really spare compared to video. For instructional content this is actually great, since you can direct the viewer’s attention to exactly the part of the screen that you want them to focus on. It reminds me of the way technical manuals always have line drawings instead of color photographs: sometimes lo-fi is BETTER if it lets you draw attention to the right information.
Also, I had pre-recorded the mp3, but I found I had forgotten to say some stuff that was really important (for example, the keyboard shortcuts for editing the beginning point of a slide, and the url of archive.org). I was able to easily add slides that had that information. PPT is a lot easier to edit than an audio file, so you can easily fill in the gaps from an audio presentation with text.
I also discovered one bug: Camtasia (which I used to create the mp3) generates mp3 files that claim to have a bit rate of 0 kbps. While the files are actually fine, the file attribute is set incorrectly, and so it was not playable by the flash player. Simply opening the mp3 file in audacity, and then exporting it again fixed the problem. Audacity is free and open source, and is a great audio recording / editing package. I’ll update our faq with this info (Update: Beth Kantor gets credit for first reporting this bug. Thanks Beth!)
The flash application for synchronizing the mp3 to the slideshow was really hard to code: I’d love feedback on it and how we could make it better. Doug Kay (from ITConversations) seemed to like it:

They have an excellent editor, written in Flash, that allows you to set the slide-transition points relative to the audio file.
Someone else wrote (in a comment):
Wowzer! That’s very powerful. I especially love the fact that I can go forward and backward through the presentation, using the slides as a visual indication of where I am in the presentation.