As I mentioned on the Cafe Mom Discussion board, I learned today that blogger now has an auto-insert picture function for the header background (e.g. the tulips above). In case you didn't pick up on the hints elsewhere, here are the directions...
You get to it by clicking on the "edit" button for the page header bar under "page elements" (which is under "template").
Add your photo and *presto*!
A couple of important tips:
You'll need to size your photo "just so" to fit with your template. Nothing like trial and error.
I would suggest keeping the photo size reasonably small - perhaps under 100 kb for the sake of those with slower-loading computers. (the tulip one is about 70 kb).
Try to get a picture with room for your title and description AND/OR adjust your blog title color so it's readable with the picture. I "photo-shopped" out two tulips to make this one fit better.
Warning: At the moment, adding the photo to the banner seems to gum up the preview mode in the "fonts and colors" window. Not critical, but annoying.