Wow! I just got done reading a blog that kind of told users an outdated way to highlight (with CSS) author’s comments. So in order to help clear up some things I’m going to break the process down. (note this is for wordpress 2.7 and up!)
THIS WEBSITE SHOWS HOW TO DO IT
I know I know… all I did was post a link to another blog that shows how to do this… But there are some things I needed to add (from my understanding):
li.bypostauthor
- using a different/custom callback function (with: wp_list_comments) will require you to code
li.bypostauthorin the new function yourself. (again, a plugin might be doing something to your callback function… So keep an eye on that) - Old themes wont support it.
otherwise, if your theme is up to date everything should go smooth by just adding:
li.bypostauthor { css comes in here }
to your style sheet as the previous link said to do 
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