[bondous] “Is it posible that FCP 5.1 imports somehow the video settings automatically?”
Nope you must convert then all to the same format before you bring them into FCP.
But your post poses some bigger issues.
Why are you editing video from the web?
Is it stick video that you purchased?
Not only is any video on the web already highly compressed and vary undesirable to work with (you always wand to pull your footage from the highest quality source possible)
If the video was not purchased from a stock video site then legally you have no right to edit it because it douse not belong to you.