Pre blog posts page summary?

Assuming I understand your request, there are a few ways to go about this without having to “rewrite some wordpress code”:

1. Use the post excerpt field for your summary and insert the_excerpt() template tag into your templates where you want the summary to appear.

In the case of providing post excerpts in your blog’s syndication feeds, these would then become your text for each post feed. If you display post exerpts elsewhere on your blog, the same applies. So consider this sort of a hack.

2. Add the summary as a custom field, using ‘summary’ as the custom key and your summary’s text for the value. Then in your templates (again, where you want to display the summary), add the following:

<?php
$summary = get_post_custom_values('summary');
echo apply_filters('the_content', $summary[0]);
?>

Not pretty, but should work. And it fulfills a WordPress coding edict of mine (try to leave the source alone!).