No problemo. If you have any of the later versions of windows (I use XP pro), do the following.
1. right click anywhere on you desktop that is not an icon.
2. at the bottom of the menu that appears, click Properties.
3. this brings up a small box titled Display Properties.
4. click the tab labeled Desktop.
5. in the lower right-hand quadrant, click the button labeled browse.
6. find you picture and make it your wallpaper.
7. the picture will appear in the virtual screen image matching the whatever the last wallpaper setting was in the Position window.
8. Click the pull down menu button for position options and pick stretch.
9. Click the OK button, and that is it.

The picture is now a full size desktop wallpaper. I have tried all three, and they work, but No 3 does get a little grainy