I think it's possible. It can take a while, but if you already designed sites, and are willing to make an effort and learn. Then you can
Maruchan's answer can seem a bit scary, but he is right, for what it seems you will have to learn a lot. I'm also a noob on cms's, and even webdesigning, so, maybe I can try to give a less scary answer
I guess your main doubt is mainly on how templates work.
Putting it in a simple way, templates let you design several pages, writing the code only once.
imagine that you have a very simple html, and all the pages on your website have the very same structure.
<!doctype html>
<html>
<head>
<title>my website</title>
</head>
<body>
<h1>My Website</h1>
<div id="sidebar">
"some code"
</div>
<div id="content">
"some code"
</div>
<div id="footer">
"some code"
</div>
</body>
</html>
What you would do to simplify your work is divide this code and put the parts that will be common to several pages in files that you can reuse. So, for instance, you can put this, on a file called 'head.inc' (i will use some dynamic content, like Maruchan explained)
<!doctype html>
<html>
<head>
<title><?php echo $page->title; ?></title>
</head>
<body>
<h1><?php echo $page->title; ?></h1>
<div id="sidebar">
"some code"
</div>
and this on another file called 'foot.inc'
<div id="footer">
"some code"
</div>
</body>
</html>
you will be left with the content div that will go on a php file, for instance 'basic-page.php' that will call the previous pieces of code
<?php include("./head.inc"); ?>
<div id="content">
<?php echo $page->pagebody; ?>
</div>
<?php include("./foot.inc"); ?>
On the backend interface, you will connect these template files with processwire templates, and assign fields to them:
title like in <?php echo $page->title; ?> is one, and pagebody like in <?php echo $page->pagebody; ?> can be another (title is present on all templates by default, but page-body i just made up).
after this you will create each of the pages of the website and assign them this template (or different ones that you can create).
This was a very basic explanation. Hope it wasn't too simplistic... there's much more complexity than this, next step could be linking to stylesheets and creating dynamic menus for instance.
Best thing you can do is play with the default installation. Open all the pages, create new fields and assign them to templates in the backend interface, and then, go to your template files and call them like this <?php echo $page->yourfield; ?>. Also have a look at all the templates that come in the default website.
And of course, read the documentation
http://processwire.com/api/
If you want to go the quick and easy way (but not as satisfying), you can also check these:
http://www.lightcms.com/
http://pagelime.com/
http://unify.unitinteractive.com/
http://www.cushycms.com/
http://grabaperch.com/
