If you wanted three ads to appear in the same place and rotate using the weighing do the following.
- Assign all three to the same banner category.
- Paste that category's cf tag where you want them to appear.
They will rotate between those banners in that category. You can set the "weight" of each ad as well. That way some ads are shown more frequently in that group than others. For more information on that, hover your mouse over the popup helper in the bannergate screen.