The tires I have are 185/60R15 Pirelli Winter Carving Edge and they fit fine. This size matches the stock tire almost exactly in terms of height.
As for the wheels, I have not heard anyone say that any 15" wheels have issues, but the brakes are a close fit on the front wheel. You can see pictures of Rodmoe's 15" wheels (I have the same 15" wheels he does, MSW Type 23) here: http://fiestast.net/threads/15-wheels-on-st.741/
Also worth noting that the 15" wheels from the normal Fiesta fit the ST