Here's how I use CSS to hide unnecessary admin menu sections for my editors who don't need to see Site Building, User Management, and so on. I'm using D6 to run a college website with multiple editors across campus.
1) Create a role for your editor. Let's have some fun with it and call it "editor".
2) In your theme's page.tpl.php file, add the user's role(s) to the body tag as classes:
<body class="<?php $userclasses = implode(" ",$user->roles); echo $userclasses; ?> >"
Obviously it's helpful if you don't have any spaces in your roles' names, but you can easily get around that with a little extra PHP (wasn't an issue for me since none of my editor roles had spaces).
3) Hide the menu items with CSS attribute selectors like so:
body.editor #admin-menu a[href="/admin/build"] { display:none; }
That's it!