The best way to find out what you should be overriding is by setting template debugging to 'enabled'.
In your settings/siteaccess/yoursite/site.ini.append you need the code
[TemplateSettings]
Debug=enabled. Ensure that this is not being overridden by a similar setting in settings/override/site.ini.append.php
You can then see exactly which templates are being called at each stage of page rendering.
Making changes to your override.ini doesn't mean that they will automatically take effect. You *NEED* to clear the ini cache. This can be done via the admin interface (setup->cache). I prefer to just delete my entire cache directory /var/cache.
Once the ini cache has been sorted out, it should work perfectly.
With the document mentioned by Tony and after Tristan's "rm -r var/cache/*" tip, the templates are now correctly used.
BTW: It seems that the 'Clear XYZ-Cache' buttons in the setup interface won't clear the cache sufficiently. Maybe someone should add extra vacuum-power in this module. :)
