There's an article I wrote in this month's Windows IT Pro magazine that provides an overview of high availability solutions for MOSS. Part of the article is available here:
http://www.windowsitpro.com/Articles/ArticleID/96301/96301.html?Ad=1 The article is brief and takes a very high level view of architecting for high availability. Over the next few months, I'll try to post in-depth on the subject, breaking it down into the different components.