Currently have:
ATO=>Style & edti HEADER AREA=>Configure Header Area:
<div id="mylogo"><a href="http://www.gc.cuny.edu"><img src="http://library.gc.cuny.edu/mrl365_2/wp-content/themes/atahualpa/images/gc_logo.jpg" alt="Mina Rees Library" /></a></div><h2 class="blogtitle"><a href="http://library.gc.cuny.edu/">Mina Rees Library</a></h2><p class="tagline"><a href="http://www.gc.cuny.edu/">CUNY Graduate Center</a></p>
%logo %pages %image


Based upon this thread:
http://forum.bytesforall.com/showthr...9927#post89927

How do I style the logo, title and taglines differently?

Do I need to do this:

<div id="mylogo"><a href="http://www.gc.cuny.edu"><img src="http://library.gc.cuny.edu/mrl365_2/wp-content/themes/atahualpa/images/gc_logo.jpg" alt="Mina Rees Library" /></a></div>

<div id="mytitle">
<h2 class="blogtitle"><a href="http://library.gc.cuny.edu/">Mina Rees Library</a></h2>
</div>

<div id="mytagline"><a href="http://www.gc.cuny.edu/">CUNY Graduate Center</a></p></div>

and then define the css on mylogo, mytitle, mytagline?
And if so where?

Also, please see:
http://forum.bytesforall.com/showthread.php?t=20562

CSS has a set of precidence - ie the order the selectors are applied. In order to apply any css to a particular HTML element, the most specific CSS selector is the one that will apply first.
You have

<div id="mylogo">
  <a href="http://www.gc.cuny.edu"><img src="http://library.gc.cuny.edu/mrl365_2/wp-content/themes/atahualpa/images/gc_logo.jpg" alt="Mina Rees Library" /></a>
</div>
<h2 class="blogtitle">
  <a href="http://library.gc.cuny.edu/">Mina Rees Library</a>
/h2>
<p class="tagline">
  <a href="http://www.gc.cuny.edu/">CUNY Graduate Center</a>
</p>

If you wrapped all that in another div with a unique ID you could use that ID so your CSS Selector will be the most specific andthe rules you code will be applied.

Shouldn't title and tagline be in their own ids, if I want to apply different CSS?

You should really take a CSS tutorial (http://www.htmldog.com/guides/css/) With the 'wrapped' div you can use that as the first selector to identify the elements.

Got that, but wanted to understand how to implement in ATO

Easy, write your CSS selector and rules and put them in the 'CSS Inserts' option which is a place to put CSS that you can't set in an option