Robert:
There's a
Pbase Wiki which has some helpful hints.
If you wish to start with just a basic banner, then all you need do is create your banner in your photo editor, I'd suggest 300 high X 800px long or bigger if you feel you can fit it in. Even though the use of 800x600 displays are declining, they still are out there so a too long banner could be a problem....but you may feel to just go with the larger screen flow and have a nice wide banner.
Once you're happy with your design, just upload the image to a hidden gallery (click off the public gallery box) and then, using html, place it in the gallery description box, using the Pbase image number in the browser address bar.
There are a few more things you can do but you are limited to html and pbase approved javascript. I use the Pbase slideshow on my root page, for example.
I used to have an image map with html but changed to my current layout. The image map can be a fun way to go, especially when the photo editor you use creates the html code automatically for you....which you simply insert into the root gallery description.
I'm sorry if this seems skimpy..but in reality most of us just learned by trial and error.
Good Luck!