Hi Brenda! I'm no good with Photoshop but there's a free website called Banner Snack which will help you create a free banner of any size. Hope this helps.
I'm a web designer and am willing to help if you still need it. I don't work for free (just really cheap), though, but I'm open to payment plans or something. Just lemme know -- my blog is www.SouthernSAHM.com (I made my own header).