Screen brightness randomly changes (Windows 7)

I installed Windows 7 last week (which has been great except for this one problem) and have had one issue arise. The screen brightness randomly darkens every couple of hours. This never happened when using Vista, so this must be some sort of Windows 7 problem. Has anyone else has this issue and does anyone know how to fix it?

Here are the specs:
Manufacturer: Acer
Model: Aspire 5810t
OS: Microsoft Windows 7 Home Premium
CPU/Ram: 1.3 GHz / 3001 MB
Video Card: Mobile Intel(R) 4 Series Express
Chipset Family
Sound Card: Realtek High Definition Audio

Desktop or laptop?
Did you try different monitor?

It is on a laptop. I haven't ever tried it on another monitor before. It happens only at random times so I am not sure how I would check it on another monitor without keeping it attached throughout the day.

how I would check it on another monitor without keeping it attached throughout the day.

I think, you'll have to put one day aside and do it.
That's the only way to find out, if there is something wrong with your laptop's display, or with the laptop itself (video chip).

Are you sure it isnt a power setting to dim the display after X amount of time of inactivity?  To check, click the little icon of the battery on the taskbar on the bottom of your computer, and click "more power options"(I think this is what it is calld" and see how many minutes it says it will dim/turn off your monitor.

Acer sometimes mirrors what Fujitsu does, is there a setting in the BIOS for what screen brightness does?

Are you sure it isnt a power setting to dim the display after X amount of time of inactivity?  To check, click the little icon of the battery on the taskbar on the bottom of your computer, and click "more power options"(I think this is what it is calld" and see how many minutes it says it will dim/turn off your monitor.

I double checked that today and changed it to a longer time than before, but the screen still randomly gets darker.