Nearly there. 
As usual, there's a ton of ways to do this; be here's an easy (untested) starter for you.
Code:
<?php
$start = isset($_GET['start']) ? strtotime($_GET['start']) : time() ;
$prev = strtotime('-7 days', $start);
$next = strtotime('+7 days', $start);
?>
<a href="/?start=<?php echo date('Y-m-d', $prev); ?>">Previous</a>
<?php foreach(range(0, 6) as $diff): ?>
<p><?php echo date('r', strtotime('+' . $diff . ' days', $start));?></p>
<?php endforeach; ?>
<a href="/?start=<?php echo date('Y-m-d', $next); ?>">Next</a>
Which should give you something like...
Code:
<a href="/?start=2012-09-17">Previous</a>
<p>Mon, 24 Sep 2012 20:45:11 +0100</p>
<p>Tue, 25 Sep 2012 20:45:11 +0100</p>
<p>Wed, 26 Sep 2012 20:45:11 +0100</p>
<p>Thu, 27 Sep 2012 20:45:11 +0100</p>
<p>Fri, 28 Sep 2012 20:45:11 +0100</p>
<p>Sat, 29 Sep 2012 20:45:11 +0100</p>
<p>Sun, 30 Sep 2012 20:45:11 +0100</p>
<a href="/?start=2012-10-01">Next</a>
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