After reading an article "jQuery Plugin: Scroll to Top" by Craig Wilson a couple of weeks ago, here is how to add it to your Blogger.
There is a similar code by David Walsh here. But I am using a code by Craig.
You can see the action in this page. You just need to scroll down a bit and you will see a ^Scrol to Top box on the right bottom. By clicking it you go to the top of the page.
1. Add the following HTML before your </body> tag.
<a href="#" id="toTop">^ Scroll to Top</a>
2. Add the following CSS code in your Blogger CSS code.
/* to top */
#toTop { width:100px;background:#F4FFBF;border:1px solid #ccc;text-align:center;padding:5px;position:fixed;bottom:10px;right:10px;cursor:pointer;color:#666;text-decoration:none; }
3. Add the following jQuery codes just before </body> tag.
<script src='http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js' type='text/javascript'></script>
<script type='text/javascript'>
/*-----------------------
* jQuery Plugin: Scroll to Top
* by Craig Wilson, Ph.Creative (http://www.ph-creative.com)
*
* Copyright (c) 2009 Ph.Creative Ltd.
* Description: Adds an unobtrusive "Scroll to Top" link to your page with smooth scrolling.
* For usage instructions and version updates to go http://blog.ph-creative.com/post/jquery-plugin-scroll-to-top.aspx
*
* Version: 1.0, 12/03/2009
-----------------------*/
$(function(){$.fn.scrollToTop=function(){$(this).hide().removeAttr("href");if($(window).scrollTop()!="0"){$(this).fadeIn("slow")}var scrollDiv=$(this);$(window).scroll(function(){if($(window).scrollTop()=="0"){$(scrollDiv).fadeOut("slow")}else{$(scrollDiv).fadeIn("slow")}});$(this).click(function(){$("html, body").animate({scrollTop:0},"slow")})}});
$(function() {
$("#toTop").scrollToTop();
});
</script>