well i wouldn't say 'simpler' if the post image thing is out of your league. thematic is uber powerful, and not to scare you off, but there IS a learning curve.
here is the definitive article on featured images:
then make sure you know how to set up child theme:
then maybe you can start browsing around in the thematic/library/extension/content-extensions.php file. all the guts of thematic live in the extensions folder (almost) and anytime I want to change something in my child theme I go there and see where it is coming from.
for instance in your case, maybe you want to change the excerpt so that it only has thumbnails? you might take a look at what is generating the markup for the excerpts... and it would be thematic_content(). and to change it you'd either filter it or use the override function that is just above it.
that should get you started i hope and you can come back with more specific questions.