There are no stupid questions. Theres just eggplant. Now thats stupid.
First off - I just updated the package. It was slightly premature so the stas thing is a bit crude... however I released it to help with debuging mysterious missing code blocks. If everyone would be so kind to install the latest version (follow the readme upgrade instructions - its pretty mild).
Now onto your Q.
Forst off... no need to stick $GAB_ads[0] in a table. Just stick it as the first line in your navbar template (you can move it about when you feel advanced

)
If you want a specific banner in specific forums, do as you suggested:
1- Create a new category (always smarter) and tick the scripts AND forums you want them in.
2- Make sure it and the scripts are active.
3- Make sure the scripts have at least 1 ad block (or better - make sure 'use master' is ticked and that has at least 1 ad block).
Thats about it. If you are still having problems getting it to appear, install the latest package and give me the debug info.
HTH's