I am personally using the same hack on this blog. You can see adsense ads below the post title on all my pages.Ok now let us get into the details of how to set it up.
First of all login to your adsense account and generate ad code of optimum size..
Now copy that adsense code into the following box and parse it(you may not see the parser if you are reading my feed)
Copy off the parsed code..
Now login to your blogger account.
Go to Layout > Edit Html and expand the widget templates.
Find this piece of code
<data:post.body/>
Now add the following code just above that line.
<!-- BloggerPlugins.ORG Adsense Above Posts start -->
<b:if cond='data:post.isFirstPost'>
Put your parsed adsense code here
<br/>
</b:if>
<!-- BloggerPlugins.ORG Adsense Above Posts End -->
<b:if cond='data:post.isFirstPost'>
Put your parsed adsense code here
<br/>
</b:if>
<!-- BloggerPlugins.ORG Adsense Above Posts End -->
From now on you should have adsense below the post title. On pages with multiple posts(eg: home page, label page etc) , the adsense ads will show up only on the first post(i.e below the post title of the first post). It wont show up on the other posts on the same page.So you are abiding by the Adsense TOS.