What would happen if you are on page 3 and have "items 24 to 36 of 50 total" ? Anyway, the code to change that is:
<div class="pager clearfix">
<p class="amount-catalog">
<?php echo $this->__('Items %s from (%s) items total', $this->getLastNum(), $this->getTotalNum()) ?>
</p>
But you should also add this text in your app/locale/en_US (and other languages)/Mage_Catalog.csv just like "Items %s from %s items total","Items %s from %s items total"
. Keep in mind my example is for english only, other languages will have the part after comma translated.
For more info look at this php function http://php.net/sprintf