You need to check your themes functions.php to see if the theme supports post images?
You are looking for a line like this:
add_theme_support( 'post-thumbnails' );
Then set the post image size:
add_theme_support( 'post-thumbnails' );
set_post_thumbnail_size( 120, 90, true );
You do not need a frame?
Then inside the loop, this might be in a file called loop.php or in your index.php
To get the post thumbnail image you need to call it:
<?php if(has_post_thumbnail()): ?>
<div class="alignleft" style="margin: 0 0 10px 0">
<?php the_post_thumbnail(); ?>
</div>
<?php endif; ?>
If your theme does not have the style “alignleft” just copy it from the twenty ten theme’s style.css file.
HTH
David