To edit the feed url, just adjust the value of
var feed_url = "/feeds/posts/default";in the code.
To know more about automated widget adding here
You can get the widget using a one-click interface here.
and below is the code
<script type='text/javascript' language='JavaScript'>
// <!--
// use this value to use Blogger's default feed
// or edit it to use other feed's URL
var feed_url = "/feeds/posts/default";
document.write("<a href='http://add.my.yahoo.com/rss?url="+feed_url+"'><img alt='' src='http://us.i1.yimg.com/us.yimg.com/i/us/my/addtomyyahoo4.gif' style='border:0'/></a>");
document.write("<a href='http://www.newsgator.com/ngs/subscriber/subext.aspx?url="+feed_url+"'><img alt='Subscribe in NewsGator Online' src='http://www.newsgator.com/images/ngsub1.gif' style='border:0'/></a>");
document.write("<a href='http://fusion.google.com/add?feedurl="+feed_url+"'><img alt='Add to Google' height='17' src='http://buttons.googlesyndication.com/fusion/add.gif' style='border:0' width='104'/></a>");
document.write("<a href='http://www.rojo.com/add-subscription?resource="+feed_url+"'><img alt='Subscribe in Rojo' src='http://www.rojo.com/corporate/images/add-to-rojo.gif' style='border:0'/></a>");
document.write("<a href='http://www.newsburst.com/Source/?add="+feed_url+"'><img alt='Add to Newsburst from CNET News.com' height='17' src='http://i.i.com.com/cnwk.1d/i/newsbursts/btn/newsburst3.gif' style='border:0'/></a>");
document.write("<a href='http://my.feedlounge.com/external/subscribe?url="+feed_url+"'><img alt='Subscribe in FeedLounge' border='0' src='http://static.feedlounge.com/buttons/subscribe_0.gif' title='Subscribe in FeedLounge'/></a>");
document.write("<a href='http://www.netvibes.com/subscribe.php?url="+feed_url+"'><img alt='Add to netvibes' height='17' src='http://www.netvibes.com/img/add2netvibes.gif' style='border:0'/></a>");
document.write("<a href='http://www.bloglines.com/sub/"+feed_url+"' type='application/rss+xml'><img alt='Subscribe in Bloglines' src='http://www.bloglines.com/images/sub_modern11.gif' style='border:0'/></a>");
document.write("<a href='http://feeds.my.aol.com/add.jsp?url="+feed_url+"'><img alt='Add to My AOL' src='http://myfeeds.aolcdn.com/vis/myaol_cta1.gif' style='border:0'/></a>");
document.write("<br/>");
// -->
</script>