@MichaelMiles-Stimson suggested [OGR2OGR][1], which is packed with QGIS. One option is to use it through command line, with the following command:

    ogr2ogr -t_srs epsg:32633 new.shp old.shp

You might prefer to call this command directly from python. [Elevine's answer][2] elsewhere shows how:

1) download [http://svn.osgeo.org/gdal/trunk/gdal/swig/python/samples/ogr2ogr.py][3] and store it somewhere in your python import path (`/usr/lib/pythonX.X/dist-packages` or `/usr/local/lib/pythonX.X/dist-packages` on Linux, not sure about Windows)

2) write following code:

    import ogr2ogr

    ogr2ogr.main(["","-f", "ESRI Shapefile", "-s_srs", "epsg:4326", "-t_srs", "epsg:32633", "new.shp", "old.shp"])

In case of bugs you might need to add full paths to the file names.

EDIT: alternative way, less bug-prone:

    from os import system
    
    #define oldPath and newPath
    cmd = 'ogr2ogr -f ESRI Shapefile -s_srs epsg:4326 -t_srs epsg:32633 '+newPath+' '+oldPath

    os.system(cmd)


  [1]: http://www.gdal.org/ogr2ogr.html
  [2]: http://gis.stackexchange.com/a/41637/12768
  [3]: http://svn.osgeo.org/gdal/trunk/gdal/swig/python/samples/ogr2ogr.py