Ok, ramming head against wall because I just came very close to the results I wanted, but then fell short.
Ultimately, I want bloggers using our website to display their blog in a totally separate theme from the main template of our site. That is, I want them to write, edit, publish, view, comment, etc entirely in, say, kubrick. But I want all other content on our site to be displayed in the custom template we have, call it Bluemarine.
http://www.cctvcambridge.org
I have tried three modules, alone and in combination, and they each do *almost* what I want:
1. Blog_theme: http://drupal.org/node/19248
This lets users who pick different viewing themes to also be the themes in which others view their content. This didn't work for me because I had to enable more than one template, and there was no promise that users were viewing our site in the template we want them to.
2. Template_theme.module: http://drupal.org/node/30135
As the author said, the themes only apply on the individual pages. So a page in the "news" category is themed, but the page that shows ALL the news items does not use the news theme.
3. Taxonomy_theme.module: http://drupal.org/project/taxonomy_theme
This one doesn't seem to work very well with clean URLs. Also, since individual entries are not deliminated by the address line (pages and blog entries are both called site.com/node/serialnumber) I can't keep up with all the ways the taxonomy changes.