This is one of those examples where you ned to purchase or build your pc to your needs, not trying to configure one after it's already bought.
I couldn't find a direct usb cable for your needs right away. However, I did find some good news.
From PCCABLES.com
http://tinyurl.com/6zmbnk - usb to VGA for extending the desktop. ((Sorry for the url frim tinyurl.com, but the one on PCCABLES is incredibly long!))
Then use another adaptor for converting vga to usb. Please note that this vga device has both an rca and a s-video.
http://tinyurl.com/6cssqw
SVIDEO-RCA to VGA Port LAPTOP
The first one is about fifty bucks and the last one is about 15