Explain how trading Helton would help Stewart in any way. It would hurt him, as he'd lose the biggest lineup protection. Helton is the face of the Rockies and will and should not be traded.
Stewart will not start this year. I was having this discussion on a Rockies board, and yes I'm very excited with how well he is doing, but this is what, 25 Spring Training at bats. He was only in A ball last year... he would not be able to handle big league pitching quite yet. Next year, yes. We'll trade Atkins in the offseason (if Stewart is ready)
Edit: BTW Shealy is trying to convert to OF for more playing time, as you don't get much behind a guy like Todd Helton. But, he got injured and its doubtful he'll make the opening day roster now.