Here's a (quite dirty) port of a pretty old (0.59r) version of an open-source MPEG Layer-3 player / decoder mpg123 based on Win32 port by Tony Million. It can be compiled using Microsoft C++ Complier (MSC) (tested in MS Visual Studio 2005). There's also a dirty-hack version of Win32 DLL for decoding mp3 files to PCM Wav, which is not tested. IIRC there are no changes to the original mpg123 except fixing Windows version and adding the DLL exports.
You might be more interested in trying current version of mpg123 and libmpg123; see the homepage: www.mpg123.de. However, it is not compatible with MSC.
The program is distributed under terms of GNU General Public License version 2 or higher, at your choice.
The current version of mpg123 available on its homepage is distributed under LGPL, but I was unable to get confirmation from the authors of mpg123 that the older version can used under LGPL as well.
mpg123-0.59r-sg.zip (142 Kb) [4944 d/l] Includes source code and Windows executable.