In general, you would want to set the .htaccess files to 666. If you set them to 777 you're allowing outside users or applications to access AND change the file. 766 setting should work ok, similar to 666, as long as "Group" and "Others" cannot execute the file.
I'll standardize this in the
Wordpress Adsense System soon. BTW, I'm thinking of making the next version video-based instead.
If that does happen, make sure you're getting all my emails regularly, as all exisitng customers will be able to get the new version for free.