How does Mac OS X 10.7 detect different displays? I have a Macbook Pro with Mac OS X 10.7, and an external display screen attached to my Macbook, which is working fine.
Sometimes, I have to switch the second display to a projector (because I want to give a presentation).

Those settings (e.g. arrangement, resolution) are different from my external display screen. In 90% of the cases, Mac OS X knows which arrangement/resolution I want, depending on the type of external screen; in 10% of the cases, it's mixing up the configurations and I have to manually edit the configuration again.

Can I see somewhere what configuration is attached to a certain display?
Why does Mac OS X mix the configuration settings between my external display screen and my projector?
1) You should be able to see these configurations in System Preferences > Display. I believe you go to to Layout (or could be called mirroring).

2) OS X displays two Display panels so you know which panel is attached to which screen.

If the Display options don't allow you to pick a resolution, change the Resolution from "Best for XX display", that will allow you to pick a supported, lower, resolution.