Choosing which export template can be tricky, especially for notes within notes. I have found that the export template specified in an include [e.g. ^include(notename, exporttempl.html)], will trump the export template specified by the child notes in their HTMLExportTemplate attribute. Keep this in mind and you can avoid the dreaded page within a page problem.
Jonty asked for more detail on how I created the righthand sidebar in my Trainblogging derived weblog. As I've mentioned before, I know only enough html to be dangerous. My usual approach is to study a template and attempt to emulate it as best I can by copying and pasting. That is what I have done here.