I have a HP Probook 6540b notebook with ATi Mobility Radeon HD4550 graphics card.
I have a problem with screen bright after install ATi drivers - is too bright.
Unfortunately, it isn't possible to correct this via Cataclyst Control Center or Windows color calibrate (I use Win7 Pro x64).
I tried install the newest drivers from ATi site and recommend drivers from HP site, but it didn't help...
Strangely, when I installed restricted drivers on Ubuntu 10 or Linux Mint 9, there weren't any problems.
So, I am sure that the drivers causing the problem.
Have you tried changing the brightness using the FN key and function keys?
Have you tried turning off or on the power savings feature that meddles with background lighting?
Have you tried using the default color scheme that comes with windows? (icm, not theme colors)
What happends if you plug in an external monitor or use a docking station?
ps. does your 6540 work properly on wireless n networks? (has nothing to do with your problem)