OK, now this is a pain. It appears I have to redo my template for the new Blogger Beta if I want to use labels. That's bloody annoying.
Update: It looks like I'm stuck for the moment. The prepacked templates are ok and can be configured, somewhat, but I prefer my old template. Fortunately the folks at Blogger Buzz say they are going to add in the edit html functionality in "days not weeks" and allow users to add labels to existing templates.