2
Hello, and welsome to XOOPS
I'll try to help with your queries as best I can.
1. Templates come with modules and these control
what is displayed within a module's blocks and on the modules index page. The XOOPS 2.3.0 download comes with a few modules (system, Protector, pm, profiles) and each of these has html templates in its /templates and /templates/blocks folders.
The XOOPS "core" uses the "system" module.
Themes control
how a module and its blocks display, i.e. the overall "look" of a XOOPS site, via a combination of theme.html and style.css
Templates will look different depending upon what theme is in use.
2. You are correct in that the default XOOPS theme uses a table-based design. However, there are a number of css-based, tableless themes available so XOOPS is certainly capable of using them.
I'm sure that someone will be along shortly to point you in the right direction