I have got the XOOPS banners in the active banners list but they are not appearing in the header. I checked the theme.html and it contains the line

[td width="100%" align="center"][div style="text-align: center; padding-top: 5px;"][{$xoops_banner}][/div][/td]

which, I presume, should display a banner. How does XOOPS chose which banner to display and how do you turn the banners on?