is there a way to turn that option off so that you can use a full image?
Well, sort of. Its a workaround.
1) Download Launcher Pro. It has the feature to disable wallpaper scrolling.
2) Set Laucher Pro to be your new default homescreen, and on the homescreen, press menu, preferences, appearence settings, and then disable wallpaper scrolling. Now when you scroll left and right between homescreens, the background will not move.
3) Start up a program like Photoshop, and create a new picture that the same height as your phone's screen, and at least 3x the width. Leave it blank for now. Preferably, keep it black so you can tell what won't be shown with the actual content.
EXAMPLE: My Droid Eris screen is 320 x 480. So I created an image that is 960 x 480.
4) Next I made an image the same size as the screen (so in my case, 320 x 480). This will contain the content of your wallpaper. Put whatever you like in it as long as it fits within those dimensions.
5) Now paste the content picture, inside the larger, background picture. Make sure its in the
exact center of the larger picture. Now you will have a picture with black side bars and your content in the center.
It will look something like this:
6) Now save the pictures and put it on your phone.
7) Tell your phone to set the picture as a wallpaper. Stretch out the cropping border as large as it can go and set it.
8) If done properly, your background picture will now be fully on the screen. There should be no black on the edges.
My end result.
Hopefully that helps.