how to show linuxmint that other monitor has different ratio

[ml2]

I cannot get the other monitor working properly in my LinuxMint system.
Computer is Dell xpsm1210 and has widescreen ratio. The other monitor has normal ratio and it is LG Flatron L1952T.
When I press Fn+F8 (Dell's button for changing between monitors), the second monitor will just say "out of range", and after pressing the buttons again (that means: "picture on both screens"), the picture comes back to Dell's screen and on the second monitor it does not fit on the screen - like it was sending the picture there with wrong settings.
I searched ubuntuforums, too, but it seems that X is not the same there and I cannot find the conf files.
1) Where's the necessary configuration file and what lines there should I see?
2) Xinerama seems to be installed from the very start, but how to use it?

Thank you in advance

[hairy_Palms]

what graphics card do you have? if its nvidia you may need to install the official nvidia drivers.

[ml2]

what graphics card do you have? if its nvidia you may need to install the official nvidia drivers.

I'm pretty sure it's Intel's integrated "card" or whatever it is called.

[hairy_Palms]

you should have a look at
http://www.ubuntuforums.org/showthread.php?t=161830
linux mint is pretty much 100%compatible with ubuntu and the xorg.conf is in the same place on both of them at /etc/X11/xorg.conf