I believe this issue is because the graphics driver for Windows 7 is not detecting that you are using a VGA to miniport cable. Please try using straight cables VGA to VGA and see what happens.
Are you dual-booting Windows 7 and Mac OS X via BootCamp? If so, you might want to consider Fusion or Parallels. They each cost between $30 and $40, but this would fix your problem without much hassle. I know Fusion allows you to port your BootCamp partition over pretty seamlessly, and I'm guessing Parallels might have that too.