Hi David,
by default, the Banner rotator web part loads a random valid banner from the specified category. If you are using banners for the above metnioned specific purpose and you would like to set a specific banner to be displayed instead of a random one, you would need to enhance the Banner rotator web part and a property, which would allow you to specify the desired banner ID.
Also, you would need to enhance the \CMS\CMSWebParts\BannerManagement\BannerRotator.ascx.cs file to reflect this property and load the banner (if set) withing the PageLoad method.
Dave