[Digital Jedi]

Yes, you can change the width of your forum to a fixed width. If your style designer didn't mess with the header template too much, then you should still be able to do that in the Style Manager under StyleVars. If not, then you'll need to edit the header template directly.

Alternatively, you could just find the CSS class where the banner is displayed and change the background-repeat to norepeat. CSS classes can be accessed in the StyleManager way down at the bottom in the custom code section. Most designers would call the banner class something recognizable and leave it towards the top. There's no one way to go about it, and no "best" way per se.