If the dimensions of your banner of 500*80 for example... Make sure that when you create your ad, you specify the exact dimensions.
I'm running openads 2.0. So if I go into "Inventory" then "Banner Properties", there is a location to set your banner "Width" and "Height". Make sure you set that to the dimensions of your banner. If you don't, your banners will no show up.
By the way for those people who complain about this not working... It works just fine on my forum. Yes, it's buggy but you can take a look at how nice it works...
http://www.njflyfishing.com.