adsense code help

im trying to follow this code but i cannot make it right.
i put that in the index.php file of my existing theme.
is there better way than this? something like a plugin?

http://www.problogger.net/archives/2006/03/09/how-to-placing-adsense-strategically-between-posts/

Note: the errro is the same is posted by Oyvind (No.33 comment)