I'm just trying to get started with SFML by using MinGW.
I have SFML 2.0 and MinGW 4.7.2 .
I'm using Code Blocks and I have the dw2 version of MinGW.
If you're really running MinGW 4.7.
2, then I think you'll have to recompile SFML, since the official version support the official MinGW 4.7 branch and the 4.7 TDM versions.
But since it's an error with strings, it might as well be, that you're mixing Debug and Release modes. When you're in debug mode, you'll have to link the debug libraries (with -d suffix) and in release mode the release libraries (without suffix).