This may be a bit of a dumb question on my part, but how do you get Heading 5 to show up? The ribbon only goes up through Heading 4. I can't add a new style called Heading 5 because the name's reserved, and I haven't yet found the handy dialogue box that shows all styles.

Ah... found a solution, maybe not the best. The "Apply Styles" dialog box (also available through Ctrl-Shift-S) will let me type in Heading 5 and then choose to apply or modify it. Annoying, but fixable.