Hi there - I'm not sure if I'm interpreting the terminology correctly ... when you say slides do you mean the "featured image" that e.g. WordPress supports to have a single image represent each post?
Unfortunately MarsEdit doesn't have explicit support for WordPress's featured images. Some folks have come up with work arounds that involve e.g. installing a custom plugin on the WordPress end to interpret either the first image in the post as featured, or to allow specifying the featured image with a kind of special coded markup in the post.
Here's an example of such a plugin, though I haven't tested it myself:
Daniel, Thanks for replying. I wasn't talking about 'featured images' though that workaround SHOULD help in THAT regard. I was referring to the slides that I have on my site www.politificating.com where when you go to the site, you're greeted with slides of stories that you click on for the main post/story.
Thanks for clarifying. MarsEdit doesn't have any built-in way to do this. It looks like possibly this is handled by a WordPress plugin you have installed? Unfortunately many of these kinds of plugin-enhancements to WordPress are not directly accessible by MarsEdit.