2 columns within a child div?

I have 2 textfields and I would like a php message to display in a once empty space to the right of the textfields upon submission.

[code=php]<?php echo $error_invalid; ?>[/code]

How can I setup this space without using tables? I already have a parent and a child div like so:

[CODE]#middle_parent {
min-width:200px;
margin:5px 146px 20px 155px;
background-color:transparent;
border:1px solid black;
padding:5px;
}
#middle_child {
background-color:#FFFFFF;
padding:5px;
border:1px dotted #2966A3;
overflow: hidden;
}[/CODE]

HTML:

[code=php]<div id=”middle_parent”>
<div id=”middle_child”>
<div id=”middle_title”>- SIGN IN -</div>
<form id=”admin_signin” name=”admin_signin” method=”POST” action=”<?php echo $_SESSION[‘PHP_SELF’] ?>”>

<p class=”style1″>username: <input name=”tfUser” type=”text” class=”style1″ id=”tfUser” size=”20″ autocomplete=”off”/></p>
<p class=”style1″>password: <input name=”tfPass” type=”text” class=”style1″ id=”tfUser” size=”20″ autocomplete=”off”/></p>

<p class=”style1″><input name=”submit” type=”submit” id=”submit” value=”submit”></p>
</form>
</div><!– close middle child div –>
</div><!– close middle parent div –>[/code]

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