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In order to install Drupal on Windows you will need to install Apache, Mysql and Php. You can do this with one simple install using Xampp. Xampp is free software from the the Apache Software foundation. Once you install Xampp, you can then install drupal on your home server.
The drupal themes/templates aren't all that easy to work with. You will need to really study the default templates in order to fully understand how they work. The best advice I can offer is look into the simplest template you can find for drupal, that way you wont have quite so much complicated code to sort through.
Hope this gives you some ideas.
That said, if you aren't fussy about having lean, clean HTML, it isn't bad to modify a drupal theme.
A good way to start is to use the Zen theme, follow the install instructions and you'll end up with, within your drupal directory (i.e. web root in most cases):
Within the "your-theme" dir (which is obviously named something more appropriate), you'll have a bunch of files, but most notably
layout.css (essentially sets the wireframe layout)
your-theme.css (typography, overrides for other styles)
page.tpl.php (the framework HTML)
Modifying those files to import the HTML and CSS from your current pages will get you pretty close to where you want to be. Because your-theme.css is loaded last, anything you put in there should override defaults elsewhere, though on rare occasions you'll need to put in a !important.
Hope that helps.
Also, the Performance panel in the admin area has a "clear cached data" button at the way bottom. That button is your friend while tweaking and debugging drupal.