Yes, template files are stored in same folder, but Joomla stores template settings in database, so each site can have different settings.
Probably except Yootheme templates because they store settings in file.

... with joomla 3, meaning I do not install the templates onto j3, rather the templates are uploaded along with j3 and content to a site's empty root folder. I want to lower my inode usage from my hosting company by shared use of joomla 3 for these sites, do you think that I can do this. I would have ...

... (which is actually under construction) - The second one at http://radio.mysite.com (sub domain which is in production, installed in a folder: root/radio/). I plan to open 3 other websites in this little network (with sub domains). I would like to share my users between all the sites. ...

... contains custom layout files for mod_login for Joomla 2.5 and 3. Extract required archive into /templates/your_joomla_template/html/mod_login/ folder (create if not exists), next select 'p8pbb' layout in login module's settings.

Joomla! should be installed in the root domain folder (i.e. http://site.com, not http://site.com/joomla/), phpBB should be installed in the first-level domain folder (i.e. http://site.com/phpBB3, not http://site.com/joomla/phpBB3/, not http://site.com) ...

... phpbb url and not yet a stable version for joomla1.7 ... Will my pages that are indexed on Google. work with this seo of the p8pbb? phpbb3 is in folder "forum" http://www.xxxxx.com/forum/viewtopic.php?f=9&t=16137 is posible to leave the original URL of phpbb3? I ask this because ...

Ok, then I have another question, to use my SSL it has to be on the primary domain so can a child site be in a sub folder without a separate domain?

and can Zoo content be shared?

1. Joomla should be installed in domain root folder and be accessed via /index.php, not /joomla/index.php 2. Joomla and phpBB should use same domains, forum.mydomain.com is not possible if Joomla is installed in mydomain.com. 3. Yes, you can convert ...

... sites in the public_html. Does this matter? Is it possible to place only one joomla site in the root "public_html" and others in a folder as in "public_html/joomla"? In the public_html there are some other folders (errors folder and stats folder) and there is a .htacces ...

Yes, you should move to folder, i.e. mydomain.com/phpBB3