You will either need to make the "cornfield" image large enough to cover any possible monitor, or do some blending in Photoshop to make the left edge match the right edge so it can tile horizontally.

If you change the urls and links to relative ones as I showed, you will be able to use/test fully while it is on your server and it will work exactly the same on your client's server without changing code (except the configure files which will have to be edited in any case.)