The output will be like this :
© Copyright 2008-2009
Note : You should update the starting year for your copyright year.
PHP Code Snippet
© Copyright <?php
$then = 2007;
$now = date(’Y');
if ($then == $now)
echo "$then - $now"; ?>
You can also try this snipper for simplity of code
© Copyright 2007 - <?php echo date('Y'); ?>
Note : You need to edit $then for setting it to the year your blog launched. The final year is automatically calculated using date() function of PHP.