Is there any way that one of you Photoshopping geniuses could help those of us who are graphically challenged?

I am having a horrible time getting a background onto my i. I couldn't get it, now I have it, but only half way... ugh. So anyways, I suppose this is a request for a small step-by-step tutorial on what to do when a Photoshop Retard (like me) is trying to make and install a background. (Also, some more specifics on DisplayOrder.plist; what to do and when and why.)
I'm not in a hurry at all, just a request

You guys are great, but I am coming to the conclusion that background is an issue quite a few have. We would all appreciate your knowledge and kindness!
Thank you in advance on behalf of all of us who can't Photoshop and/or follow your already great instructions!