Hello, my laptop like many others have the FN buttons to increase and decrease brightness. However, the lowest setting isn't dim enough for me. I believe I have found a software that rectifies this problem, but it is for Mac and not Windows Vista (http://www.splasm.com/brightnesscontrol/index.html).
See if this works. It is called DimScreen and it is freeware. It will dim the display in increments of 10% (from 10% to 100% brightness).
However, this is exactly what my Fn key will do on my laptop. So, I don't know if it will be any different for you. Count how many brightness increments you have when using your Fn key. I have 10 (from 10%-100%).
I find that 30% brightness is a comfortable setting while conserving battery usage.
