Hey there, Barcelona is a load of fun... just watch your bag and wallets on la rambla. I don't know if people around us got unlucky but 1/5 of the people we met had something stolen!
But don't despair, it's one of the nicest place i've been to in europe. Don't miss the park guel and la sagrada familia, they're fabulous. Also buildings made by gaudi are very nice :-)
Also, if it runs at this time of the year, go see "la place de espagna" with the fountain show outside for free every night, it's crazy! :)
take a look at my pictures, it might give you some ideas:
http://www.totalworlddomination.org/gallery2/v/ete06/barcelona/
cheers! have fun!