SquirePC,
There is no correct size, just because I've sized my banners the same doesn't mean that you need to create them the same size...
If you want to use my size as a template, simply right click on my banner and save it to your desktop. then open it into your graphics program and use it as a template. I usually double the size when I'm working on the graphics then shrink it back down when I'm ready.
Hope that's a help.
Jules