Can I open GSM files in Rhino?
From the Rhino 3D site http://www.rhino3d.com/features/
So, the answer is no. If you can export from the application that produces GSM files (ArchiCAD?) in IGES or STEP format (two commonly used interchange formats) this can then be imported into Rhino.
Out of curiosity: are you referring to ArchiCAD Library files (.gsm) or some other format?