I recently purchased a lenovo G580 laptop. It does not have a separate graphics card.
I also installed ubuntu and windows 7 64 bit . Lenovo provided a driver cd for windows 7. I installed all the drivers. The lenovo FN+up and down brightness control works fine in windows 7. But it does not work in Ubuntu. When I press the key combination, the brightness control appears and it shows the brightness is decreasing or increasing, but actually nothing happens. As i am new to linux, I did some search in the forums and found out two solution.
1. changing the etc/default/grub file to modify the entry
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=video"
2. changing the XOrg.conf file (which does not even exist in ubuntu 12.04)

None of these worked for me. If you experts have any known solution, please share it with me.

Thanks.