If you have switched your blog from older blogger to new blogger platform (which uses layouts) and looking for adding adsense advertisements in between posts; Blogger has created a new widget for this purpose. And they have made it such that any non-tech blogger even can use this. This widget lets you specify number of posts between an adsense advertisement. You can see the full guide here at Get inline.
If you haven't switched to new blogger yet, don't worry. You still can put adsense ads between your posts. You have to put the adsense code inside the tags that shows up the blog post. My home page has done like that. If you need any assistance on that, just drop me a mail or write below as a comment. I would be happy to help you.