The new template language is completely different from the old one. So even if you're used to working with classic templates, you'll need to learn some new tricks to directly edit the new templates for Layouts-enabled blogs.
I have a feeling that this weekend I'll be up to my armpits in blog templates! I can't wait! For those of you also interested, here is a link to this announcement on the beta blogger blog: http://buzz.blogger.com/2006/08/new-old-feature-on-beta.html
P.S. This is post 199½!