The Big Nutts dude that created this plugin is apparently not taking care of his site as it is down.
Adsense injection is pretty easy and works in WordPress as a plugin
Anyway Adsense injection is easy to install, just extract the one file into the /wp-content/plugins directory and then enable it. You need to feed in your adsense code and the size of adsense block that you want on each page and you are done!
Let us know your results. I have used this for a 400% increase in my adsense clicks and earnings (Google you ok with me saying that?).