Vidic says their 2009 defeat in Rome still burns.
"We are celebrating but everyone is thinking about the next game. It is the biggest game of the whole year.
"We know what it feels like to go to the final and lose. It was one of the saddest moments of my career. I am sure all the players won't forget that.
"We know we are facing a very, very good team and we have to be physically and psychologically ready. Against this Barcelona team you have to be intelligent.
"They have qualities but we will try to work on their weaknesses, expose them and try to win the game."
Manager Alex Ferguson has been thinking about Barcelona ever since the disappointment of that final defeat in Rome.
United find themselves in the rare position of being underdogs but Fergie remains unfazed. He said: "Yes, I concede Barcelona are favourites in many people's eyes and have a super side, rich in experience and yet youthful enough to give them a good balance.
"But it is a challenge we are eager to meet. Don't write us off.
"We have the players to win, too, and while praising Barcelona is something that comes naturally, we will be making our own contribution."