Luckily there's not a lot of implementation specific stuff in SICP, so you can probably use any Scheme you want. But I think it was written with MIT scheme in mind. MIT scheme is free (and actually it was one of the really early pieces of free software in the FSF sense- I think Sussman is still on the FF board.)
Anyway, I doubt you'll run into a lot of issues like this in SICP, so there's no big reason to switch if you like Dr. Ed, etc. But you could also use MIT Scheme. You'd probably want to use Emacs for that, but I think it's not a bad idea to get used to emacs if you want to do Lisp. I've never been very crazy about Dr. Scheme's user interface, and I find it hard to imagine actually doing real work in it, though YMMV.
Anyway, like I said, it probably doesn't make much difference. I actually got a friend of mine going in CL by installing Lispworks on his laptop and then working through the first parts of SICP in CL with him. Part of what's nice about SICP is that it deals in the eternal verities a lot more than it deals in the specifics of the platform.