Hi Irian,
Unfortunately, you cannot open SW2001+ files directly in SW2001. However, you can export this model in another extension, like Parasolid, IGES, STEP (3D Parts or assemblies) or DWG / DXF (drawings) and open it in an earlier version. In these cases you are going to loose the features of the model.
I recomend you use the Parasolid extension. It´s faster, smaller and safer.
Regards,
MHendler