Rizos! I was unable to reply to your email! My group had no problems in Spain with anti-war /anti-American centimate. In fact, the Spaniards we met and talked with expressed more curiosity about our feelings towards the war and our president than hostility. However, we are young 20-somethings, so I'm not sure how much that effected our responses.
Our hotel in Madrid (Hostal Adriano) is near Puerta del Sol where one of the largest protests were held, and it was a bit nerve wracking at first, but we experienced no ill-will.
Still, I wouldn't go around sporting an American Flag or pro-Bush t-shirt!
Have a great time.