Using query_posts() function

Can anyone spot what I’m doing wrong? Take a look at this Page

https://www.sbox.net/blogrd105/?page_id=126

I’m building a custom Page template. I’m trying to use query_posts() with a custom query string, like this
<?php $testDate = ''2005-02-23 23:59:59''; ?>
<?php $theQuery = ''post_date>' . $testDate . '''; ?>
<?php query_posts($theQuery);???>

Without our using string variables, the code would look like this
<?php query_posts('post_date >= '2005-02-23 23:59:59''); ?>

So far, I haven’t been able to format the parameter for query_posts() properly – at least that’s my theory. What am I doing wrong?