Typically, I had to do this to modify the DZone plug-in which had some ugly configuration to modify the post subpanel in the WordPress administration page.
Then, here the few things you need to do to create a beautiful meta-box within any WordPress post page
This code will works for any version of WordPress 2.x. Since wordpress 2.5, a new API has been defined to allow easily to add admin meta-box but if you want to create a plug-in compatible with older version of wordpress, here is the way…
First in your plug-in page add this piece of code. It will direct wordpress to listen any event of adding more stuff in the post page :
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add_action(‘dbx_post_advanced’, on_meta_boxes_added);
This step done, you need to write a php function which will handle this “event” :
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<?php function on_meta_boxes_added() {
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add_meta_box("divId", "DivName", "write_meta_box_content", "post");
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} else {
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?>
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<fieldset id="divId" class="dbx-box">
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<h3 class="dbx-handle">DivName</h3>
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<div class="dbx-content">
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</div>
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</fieldset><?php
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}
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}
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?>
You just had now to write your own “write_meta_box_content” function.
Of course, using WordPress 2.5+, by adding an “event” to the action “do_meta_boxes” you can add meta-boxes everywhere they are used.
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add_action(‘do_meta_boxes’, on_meta_boxes_added, 10, 3);
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function on_meta_boxes_added($page, $type, $post) {
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echo "$page admin of $type contains $post
"; -
}
Here, as you can see, my admin post page look good now

For those of you who would like to have the modified plug-in working directly here is the link :
Re: First in your plug-in page add this piece of code. It will direct wordpress to listen any event of adding more stuff in the post page :” What do you mean, “your plug-in page? What is this exactly? What page? Where?
Sorry, I am using WP 2.9.2 now. Your guide was for older versions. As you mentioned, “Since wordpress 2.5, a new API has been defined to allow easily to add admin meta-box .” So can you point me in the direction of where I would learn to take plugins that use the new WP CORE Custom Field Meta Box and create their own meta box for each of the scripts I want to make separate meta boxes for?