a quick screencap ofwhat this mod looks like in the admin panel. All you really can't see is just the bottom where they're only a button that changes the banner after you select it. Not shown in that cap is that in the board config page, there's two fields added in where you can change the path of where your forum banners are located relative to the root phpBB directory, as well as a field to change the number of columns shown in the change banner page to optimize it for each admin depending on their resolution and banner sizes so they're not set to having only two columns displayed when many more can be on their screens.
As for the errors coming up, I'm not too sure of what could be causing them, I would either try inserting each SQL line one at a time, or using phpMyAdmin to enter them in if the SQL is being a problem. Also make sure that your images/banners folder has the logo_phpBB.gif file in there so the code picks up at least that file to get started. If there's any more problems, please post and I'll try my best to help out.