Their is a program called Multiscape that would automatically do what Chealion explained by getting your screen dimensions and automatically sizing and splitting the wallpaper. Although the google code page is down. If you want to go on a treasure hunt Multiscape is what you're after.

How can I span wallpapers over two monitors in Mac OS X?
can anyone come up with multifunction laser printers available in India that work with Ubuntu 12.04? I'm asking because on most websites, I can't seem to find the models which are available on Indian markets/shopping websites. I know that sometimes that does happen, because new models replace old ones at a delayed schedule here.
