The 2008 articles are just starting to hit the web. This one deals with migration, not upgrading. You can't upgrade to 2008 Failover Clustering. I am actually glad you can't upgrade, I really don't like that word.
Here is the article: http://technet2.microsoft.com/windowsserver2008/en/library/6820ae3f-1ecc-43fd-8a76-fe8c2125cfe61033.mspx?mfr=true