arcgis 10.0 - Adding new group layer with ArcPy?

Does anyone now how to add a group layer with Python in ArcGIS Desktop 10?

I can use arcpy.mapping.AddLayer but surely this is only for an actual layer as opposed to a group layer.

so far I have this

import arcpy
mxd = arcpy.mapping.MapDocument("CURRENT")
df = arcpy.mapping.listdataframes(mxd, "layers")[0]
arcpy.mapping.AddLayer