What is Macbeth's reaction to the witches' "news," and does this change when he finds out he is the Thane of Cawdor?

Initially, Macbeth is incredulous; he cannot believe what the Weird Sisters have told him.  He wants them to keep talking and to tell him more, including how they know the information they claim to know and how they came to meet with Macbeth and Banquo on the heath.  When the witches vanish, Macbeth is awestruck and says that he wishes they had stayed to answer his questions.  Banquo wonders if he and Macbeth were hallucinating when they saw the weird women, and the pair of friends seems to joke about the oddness of the experience. 
However, once Ross and Angus tell Macbeth that he's been named the Thane of Cawdor, Macbeth expresses confusion, but then he begins to hope (privately) that the sisters' other prediction would come true.  He says, "Two truths are told / As happy prologues to the swelling act / Of the imperial theme" (1.3.140-142).  He refers to the fact that the Weird Sisters were right -- he is the Thane of both Glamis and Cawdor now -- and so he begins to think that he cannot but become king (the "imperial theme"), as they said he would.  In other words, he goes from disbelief and shock to acceptance and certainty.