You could just create a edit control and scroll using a thread (or windows timer). On every time increment you would do:
SendMessage(hEditControl, EM_SCROLL, (WPARAM)SB_LINEDOWN, 0);
However scrolling an edit control like this will move a whole line at a time so it won't look very smooth.
You could play with SCROLLINFO structures to get pixel level motion by scrolling.
There's also ScrollWindow() which would probably work.
You could also make an image of the credits and paint the image in to a static control then move it (or use an animation control(?)).
Finally, there's probably some code out there from somebody who's already done this.
--Will Duty
wduty@radicalfringe.com