The "wave" lessons have been moved to Google Docs, which is more usable and accessible. Here's where to go to edit them:
Since this exists, Lindar wants a link to it.
Since google wave has been opened up to everybody recently, you can now access the wave lesson on google wave itself, by following this link to google wave.
if, for some reason, you need the old wave lesson html export that was here previously, look here.