Mate of mine said if anyone's built to beat Barcelona at their own game (i.e. without doing an Inter '10 or United '99 on it), it's Arsenal. I can sort of see what he means.
Your mate is a complete moron then and doesn't understand, errm, football. The teams that are "built to beat Barca" are those with bagloads of pace and incredibly quick counter attacking, for Wengers early successful years that was 99% what our game was based on. These days our game is based on Denilson/Diaby/Song sideways passing for a few minutes before daring to go forwards. WE have one uber fast player, who can't cross, pass, dribble to save his life, and no other real pace at all in the team.
Barca only get hurt when people catch them on the break, and it generally happens when they have 8 players in the opponents half and Puyol/Pique around the halfway line, considering Pique is one of the worst ever defenders to be a starter at a top four club in ANY league, anyone has a chance for a lucky result against them, but even then Barca will normally outscore you badly.
Arsenal have a ridiculously small chance of doing well. We've got, realistically a single player in Fabregas who can play at Barca's level, and without people around him to pass to, its not all that worthwhile.
Also despite some deluded Arsenal fans, we've got a noticeably worse CB pairing that will probably play in the game. Well we can't match Gallas/Verm at all, but if Verm isn't back by then, any two we put out will be a joke in comparison.
Brentford could theoretically beat Barcelona, anyone can beat anyone anytime and anywhere. If pique has one of his bad games and scores an own goal then gets sent off while conceding a penalty, who knows. Realistically, I only hope we lose by a margin of less than 5, and only then so I can laugh at Mourinho.