Our server recently crashed and we lost our google adsense and a flash ad module. I didn't put it up initially, I'm just trying to figure out how to get it done.
It depends upon how want it, you can either put directly it in index.template.php creating new colum on left side or use one of the ad management mod for SMF from smf mod site. Generally I simply append theme file to place ads.
So get your code from google and place them in your theme (location depends upon your theme).