My header banner is a PNG image - is it possible to add a small .swf image to the end of the banner

yes, because you're on default templates, I would just go into the template file you're using and add the line of code directly to the template file (html).
 
I have my header section on a template divided into 3 sections, so it's easier to place blocks in the header.
 
Either way, just modify your header template file.

Thanks, I'll find a moment to look at this - I have the notion to put my clock to the right of my banner