Ok - I think I'm getting close to it now:
Make a copy of the following file and then open it in your text editor:
/wp-content/themes/default/index.php
Find the section that looks like:
<div id="content" class="narrowcolumn">
<?php if (have_posts()) : ?>
then replace it with:
<div id="content" class="narrowcolumn">
<?php query_posts('p=1&cpage=1'); ?>
<?php if (have_posts()) : ?>
Then find the section that looks like:
<div class="entry">
<?php the_content('Read the rest of this entry »'); ?>
</div>
then replace it with:
<div class="entry">
<?php the_content('Read the rest of this entry »'); ?>
</div>
<?php comments_template() ?>
(The code above was taken from the comments.php file in the same folder.)
This hack is a bit of a fudge because it messes up the sidebar code (some of the links don't appear as normal) and it doesn't have all the commenting controls. Plus, when you leave a comment it takes you to an ugly URL like:
http://www.mydomain.com/wordpress/?p=1&cpage=1#comment-11
which kind of gives the game away. Some kind of SEO-friendly plugin would make everything look a bit nicer.
Not quite the comprehensive solution I wanted but it's a start :)
Neil