Hi Scott,
You can override the template file item_comments_form.php and comment these lines:
<label class="formUrl" for="commentURL"><?php echo JText::_('K2_WEBSITE_URL'); ?></label>
<input class="inputbox" type="text" name="commentURL" id="commentURL" value="<?php echo JText::_('K2_ENTER_YOUR_SITE_URL'); ?>" onblur="if(this.value=='') this.value='<?php echo JText::_('K2_ENTER_YOUR_SITE_URL'); ?>';" onfocus="if(this.value=='<?php echo JText::_('K2_ENTER_YOUR_SITE_URL'); ?>') this.value='';" />
When you comment them, the url field will not be displayed.
