Kobus,
The easiest way to accomplish this is to use either the pathauto module (http://drupal.org/node/17345), or my hierarchical aliasing patch (http://www.greenash.net.au/posts/thoughts/hierarchical_url_aliasing), to create hierarchical paths for your nodes (and terms) based on taxonomy. You can then use the sections module (http://drupal.org/project/sections) to apply a different theme to all parts of your site that start with a certain path.
I tried out using my patch, in conjunction with the sections module, on a development copy of my site (which is running 4.5). I created a new section, set its pages to be "services*", and then everything under the 'services' term on my site (i.e. nodes, child terms, and the root term itself - I would have done "services/*" if I wanted everything but the root term) suddenly had a different theme! I got this working within 5 minutes.
Jeremy.