I have Ubuntu 12.04 installed on my VAIO S series (VPCS149FJ) that came originally with Windows 7 SP1. I installed it with Wubi.
I can't change brightness in Windows with the Fn+F5, Fn+F6 hotkeys and not even from the Control Panel. I recently did a Windows reinstall but I believe I have the proper keyboard driver (Fn+F3, Fn+F4 works for volume control) and proper monitor driver (Generic PnP monitor matches the Monitor layer in the fully expanded Device Manager screenshot provided by VAIO).
However, in Ubuntu I can change brightness in the preferences, and the unchangeable brightness in Windows is much darker than the default brightness in Ubuntu (set to the brightest).
I've looked for information about this issue in Ask Ubuntu but all I can find is that brightness doesn't change in Ubuntu, not in Windows.