try http://www.satollo.com/english/wordpress/include-it it’s a script that lets you place iframes in posts and pages. It worked for me, but it is a little limited.
I hope this works for you or is what you are looking for.
another solution might be to create a custom page template with the iframe script in it.
To learn more about custom page templates read http://codex.wordpress.org/Pages#Creating_your_own_Page_Templates
example (This is from my k2 theme):
<?php
/*
Template Name: Custom Page With iFrame
*/
?>
<?php get_header(); ?>
<div class="content">
<div id="primary">
<div id="notices"></div>
<a name="startcontent" id="startcontent"></a>
<div id="current-content" class="hfeed">
<?php while (have_posts()): the_post(); ?>
<div id="post-<?php the_ID(); ?>" class="<?php k2_post_class(); ?>">
<div class="page-head">
<h2><a href="<?php the_permalink() ?>" rel="bookmark" title='<?php printf( __('Permanent Link to "%s"','k2_domain'), wp_specialchars(strip_tags(the_title('', '', false)),1) ); ?>'><?php the_title(); ?></a></h2>
<?php edit_post_link(__('Edit','k2_domain'), '<span class="entry-edit">','</span>'); ?>
</div>
<div class="entry-content">
<?php the_content(); ?>
<iframe align="right" SRC="http://www.example.com" TITLE="Example of iFrame Usage" width="100%" height="1000px" scrolling="auto" frameborder="0">
Sorry. If you're seeing this, your browser doesn't support IFRAMEs.
You should upgrade to a more current browser.
</iframe>
</div>
</div> <!-- #post-ID -->
<?php endwhile; ?>
</div> <!-- #current-content -->
</div> <!-- #primary -->
<?php get_sidebar(); ?>
</div> <!-- .content -->
<?php get_footer(); ?>
I’ve used custom templates with iframes and scripts, such as javascript calculators, and it has worked great for me.
Good luck, I hoped this helps.