I've got the same problem you have, and I'm not au fait with php scripts and .css yet either.
Today I discovered an add-on that allows me to add Adsense semi-automatically to every page or comment I add to the blog. (See http://www.beefly.info/blog/ to see what it looks like.)
The Adsense Deluxe 0.4 from Acme Technologies Zeitgeist who are at http://www.acmetech.com/blog/adsense-deluxe/
Just upload it as per the instructions and then load the adsense code from Google into the program's setup. It's easy, and you can select any size/shape as your default ad.
Then you create or edit a document... And you'll see in the top right hand corned of your Editing window there's an option to select one of the Adsense codes that you grabbed off Google.
It drops a code like <!-- adsense --> into the text you are writing, and when the page is created and viewed - there's your advert.
It's a start. But I do want to find the right way to have fixed ads built into the template and particularly the right margin... Any suggestions anyone?