I am using 4.8.1 SDK and Qt Creator 2.5, so things may be a little bit different for you...
This works for me:

1) install Debugging Tools for Windows
2) in Qt Creator: Tools > Options > Debugger > Source Paths Mapping - add:

Source path: c:\iwmake\build_vs2010_opensource_________________ PADDING_________________
Target path: c:\QtSDK\QtSources\4.8.1

I found source path by looking for some "path-like" strings in PDB files under c:\QtSDK\Desktop\Qt\4.8.1\msvc2010\lib.