In the discussions and instructions on this site we use the terms "template", "theme" and sometimes "skin" interchangeably - don't let this throw you.
We'll try and keep the focus of this site on our specific tasks - template setups and migrations... so we won't be discussing elementary or general HTML and CSS rules, CMS basics and so on.
The #1 rule:
We are migrating static websites onto the CMS in order for the site owner to be able to easily edit his content. If faced with a choice between "looks just like the old site" and "easy to edit the content", ALWAYS choose "easy to edit".
Suggested path to enlightenment: