Custom Banners

My website is looking a little tired, I want to razz it up and have
created a custom border in Publisher with fade effect and a washed out
photo. I've only ever created websites using FP themes before, how to
I add this banner to the site in a way in which it will stretch to the
edges of the screen (i.e. behave like a banner). I tried making my own
theme, but the graphic came out huge. I want to make new link bars
too, should I create a new theme?

Help,
Janet