Display Brightness Adjustment Issues

I recently have been updating trying to update the graphics chipset drivers on my Inspiron 1520. I've been battling with different drivers for at least a week now, but I haven't figured it out yet. My display adapter is a Mobile Intel 965 Express Chipset; right now, I'm running with driver version 7.14.10.1409, from Dell's driver downloads for my chipset. The problem is, when I adjust my screen brightness (either with the keyboard or the OS controls), the display's brightness doesn't scale properly. What I mean is that each increment of the brightness is not one step brighter/dimmer than the previous/next. When adjusting the brightness from the Windows Mobility Center (I'm running Vista), the screen is brightest at 100 and 24; at 12 (the lowest I can go), it is marginally dimmer than 100/24. It's darkest at 36. 100, 84, 72, 60, and 48, seem to be correct. Finally, 12 and 84 seem to be the same.

I've tried drivers from Intel, but that didn't help. My last step was to uninstall the graphics drivers, so I was running on a generic VGA Windows driver, at 800x600 res. Then I installed the Dell driver.

I know this all may not make sense; if more info is needed, I'll be happy to give it a shot. I'd really appreciate help in figuring this out. As a final note, I started playing with the drivers just before installing Vista SP1; I didn't notice the problem until after SP1 was installed, but it's possible (likely?) that the problem was there before. Also, I dual boot with Ubuntu on the laptop, and the screen brightness works fine in Hardy Heron 8.04.

TIA,

Andrew

EDIT -- When running on the generic  VGA Windows driver, the brightness adjustment worked perfectly.