I have finally given up on my dual-screen attempts until further notice.
The reason for this is not a software issue, but a hardware issue. No, my graphics card hasn't blown up or anything like that. What I failed to mention in my previous post about dual screening, is that the LG I had on the left did not have DVI. Who in their right mind would leave out DVI on a fullHD monitor? What were you thinking, Goldstar? And yes, that's what the monitor was identified as when I looked in the display settings.... Goldstar...
The biggest beef I had with LG's VGA-only screen is that it causes confusion in dual screening because my Samsung (the screen on the right) is plugged in with DVI. In Windows 7, there is no problem here because Windows "magically" sorts out all the confusion. Ubuntu, on the other hand, with the proprietary ATi Drivers, could not seem to understand what the heck was going on! I screwed around with it for about half and hour until I gave up.
The confusion: ATi's drivers was adamant that the LG was on the right... no matter how many times I told it that it was on the left. I even swapped the plugs at the back of my PC and they were still swapped around. Secondly, the LG would only accept sizes up to 1600x1200, which is not it's native resolution. In fact, FullHD wasn't on the list at all! If I changed any setting, wither it would screw up X and make it unusable, or it would tell me to reboot. After rebooting, however, the problems started from square one again, namely the monitors being swapped around all the time!
In the end I ripped out the LG in anger and threw it across the room, vowing never to buy LG ever again! Not actually, but I was very angry at both ATi, for their lack of consideration of Linux users, and LG, for their ignorant negligence. Do the world a favour LG, go back to making washing machines!
So, to summarize, if you're looking to do any kind of dual-screening, make sure both your screens use DVI inputs*, otherwise you are going to find yourself in some serious trouble. Even better, both your screens could be the exact same model, could you imagine that!?
See my previous post about dual-screens.
*You could also have them both use VGA inputs, but who in their right mind... ?