From my understanding QGIS 2.0 does not have that ability. Other may know better, but I heard it will be available in future releases. An option would be to use PostGIS 2.0, which has 3D geometry as an option.
GRASS GIS 7 tool from the Processing Toolbox. In this tool you can select your input vector map (shapefile) and define the attribute column which holds the elevations. After the processing your features have real z values.