lol Does it have to be those exact dimensions? I might be able to do one at work tomorrow if I'm not too busy, I don't have photoshop on my laptop.
Right click on the middle of the banner and save as. Notice it has gradient on the left/right so it matches up with the stretched background behind it. The top banners are three pieces: a 1 pixel wide (about) 90px tall gradient that is stretched as wide as the browser, the logo in the center, and the "powered by" on the bottom left.