Saruman for or against Sauron?

Originally Posted by William Cloud Hickli

I believe you've been led astray by the movies. Denethor knew nothing of the Ring, nor did Boromir or Faramir, when the elder son departed. He was merely enquiring as to the meaning of his strange dream (wherein 'Isildur's Bane' is not clarified, and indeed Boromir thought it might be an Orc-arrow)

I believe you have made a mistake here - recall the words of Boromir when the Ring was presented to the Council. He desired to use it for the war against Mordor. Also, recall the words of Denethor on his son's role :"He would have brought me a mighty gift".