I renamed my small Explorer add-on "3DGS Shell Extensions" to the "3D Shell Extensions" because it supports now not Acknex MDL files only.
You may preview 3D model files in all major Windows shells or in the standard "Open" dialog:
-Acknex MDL (all types)
-Autodesk 3DS
-BlitzBasic 3D
-Milkshape 3D
-Microsoft X
-Quake MD2

Visit http://lion-ts.com for details.