I'm using a Dell Vostro 2510, and just installed Windows 7 Ultimate.
I managed to install Dell's Quickset app, all keyboard functions work now, except the brightness... it will show the little progress bar but the brightness itself doesn't change.
My BIOS doesn't allow me to change any settings regarding brightness, I can't find it anywhere!
In the Boot tab of the BIOS I only get a list of: Hard Disk, CD Rom, USB and some other devices, but nothing related to brightness, thus, this solution doesn't work for me, screen is about 75% bright, its bearable, but not for my taste, and I can't dim it all the way down using Power Saver plan or put it all the way up in High performance plan because the control won't show on Power Plan settings (not even in advanced power settings).
The brightness control worked when I had Vista installed.
I'm still looking for a solution :S
Edit: I'm going to download the chipset drivers from the Intel website and also the win7 nVidia drivers for the GeForce 8400M. I hope that resolves the issue
Edit #2: Finally, it worked, I installed the drivers for the nVidia GeForce 8400M and also the latest Chipset drivers from Intel 900 series. I'm so happy!